<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:db5948dc-9d9a-4f76-9f8c-a863f22c6dfb,g:057e645f-6672-46b5-a969-9d7607cac9f6-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.curis.com/role/CondensedConsolidatedStatementsofStockholdersEquityDeficit" xlink:type="simple" xlink:href="cris-20250630.xsd#CondensedConsolidatedStatementsofStockholdersEquityDeficit"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/CondensedConsolidatedStatementsofStockholdersEquityDeficit" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_9e4ed4e2-961b-40dc-b157-1a0ff4f5b4e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_d57858c3-0065-4dda-9a2f-501da5f41cca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9e4ed4e2-961b-40dc-b157-1a0ff4f5b4e2" xlink:to="loc_us-gaap_StatementTable_d57858c3-0065-4dda-9a2f-501da5f41cca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_8647f852-ade9-471c-8611-78ed199a94a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d57858c3-0065-4dda-9a2f-501da5f41cca" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_8647f852-ade9-471c-8611-78ed199a94a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8647f852-ade9-471c-8611-78ed199a94a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8647f852-ade9-471c-8611-78ed199a94a6" xlink:to="loc_us-gaap_EquityComponentDomain_8647f852-ade9-471c-8611-78ed199a94a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_3f0c254c-6ff9-47d6-8957-6632e1bfda8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_8647f852-ade9-471c-8611-78ed199a94a6" xlink:to="loc_us-gaap_EquityComponentDomain_3f0c254c-6ff9-47d6-8957-6632e1bfda8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_29941ea7-b8ba-43eb-b10c-27fd7efd7821" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_3f0c254c-6ff9-47d6-8957-6632e1bfda8a" xlink:to="loc_us-gaap_CommonStockMember_29941ea7-b8ba-43eb-b10c-27fd7efd7821" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_c5d8c3c1-35ad-4de9-9418-d2048dae3dca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_3f0c254c-6ff9-47d6-8957-6632e1bfda8a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_c5d8c3c1-35ad-4de9-9418-d2048dae3dca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_5184225e-c890-4d88-9070-307309850292" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_3f0c254c-6ff9-47d6-8957-6632e1bfda8a" xlink:to="loc_us-gaap_RetainedEarningsMember_5184225e-c890-4d88-9070-307309850292" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_031e7312-1fa6-4479-810d-4f3ca069e2ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_3f0c254c-6ff9-47d6-8957-6632e1bfda8a" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_031e7312-1fa6-4479-810d-4f3ca069e2ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_37bbb565-50ed-4fa4-8f4d-324b7e740f26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d57858c3-0065-4dda-9a2f-501da5f41cca" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_37bbb565-50ed-4fa4-8f4d-324b7e740f26" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_37bbb565-50ed-4fa4-8f4d-324b7e740f26_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_37bbb565-50ed-4fa4-8f4d-324b7e740f26" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_37bbb565-50ed-4fa4-8f4d-324b7e740f26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_6be465ca-a281-4a1d-8782-00b49eb7fe41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_37bbb565-50ed-4fa4-8f4d-324b7e740f26" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_6be465ca-a281-4a1d-8782-00b49eb7fe41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PreFundedWarrantsMember_91dc2101-6569-40f5-943b-359636569037" xlink:href="cris-20250630.xsd#cris_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_6be465ca-a281-4a1d-8782-00b49eb7fe41" xlink:to="loc_cris_PreFundedWarrantsMember_91dc2101-6569-40f5-943b-359636569037" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_c541b521-2c5a-4afa-b670-a419fb7d26b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_6be465ca-a281-4a1d-8782-00b49eb7fe41" xlink:to="loc_us-gaap_WarrantMember_c541b521-2c5a-4afa-b670-a419fb7d26b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9e4ed4e2-961b-40dc-b157-1a0ff4f5b4e2" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_08d69dc4-6b7f-410c-994d-7a80fc4e464b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_CommonStockSharesIssued_08d69dc4-6b7f-410c-994d-7a80fc4e464b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a885229e-3378-4f91-8075-de4a4f199787" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_StockholdersEquity_a885229e-3378-4f91-8075-de4a4f199787" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_d3d91d53-f491-4955-a497-dc2babbd5f20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_d3d91d53-f491-4955-a497-dc2babbd5f20" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_93a17eaa-5820-452d-828f-c826f3d355da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_93a17eaa-5820-452d-828f-c826f3d355da" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlansNetOfSharesReceivedForTaxObligation_13f3c79a-6496-416a-9c04-b8f41d71c9d3" xlink:href="cris-20250630.xsd#cris_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlansNetOfSharesReceivedForTaxObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_cris_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlansNetOfSharesReceivedForTaxObligation_13f3c79a-6496-416a-9c04-b8f41d71c9d3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlanNetOfSharesReceivedForTaxObligation_1047ce8a-d095-413b-a1fb-240bae73654b" xlink:href="cris-20250630.xsd#cris_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlanNetOfSharesReceivedForTaxObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_cris_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlanNetOfSharesReceivedForTaxObligation_1047ce8a-d095-413b-a1fb-240bae73654b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan_5bd8d272-a40b-4f11-8be2-269ed60562cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockOwnershipPlan_5bd8d272-a40b-4f11-8be2-269ed60562cc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_e543e1cb-3c4f-42ad-8f29-0d095daa8a05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited_e543e1cb-3c4f-42ad-8f29-0d095daa8a05" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockIssuedDuringPeriodSharePreFundedWarrantsExercised_9b9eca18-fa39-46e0-b52b-4a156a082751" xlink:href="cris-20250630.xsd#cris_StockIssuedDuringPeriodSharePreFundedWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_cris_StockIssuedDuringPeriodSharePreFundedWarrantsExercised_9b9eca18-fa39-46e0-b52b-4a156a082751" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockIssuedDuringPeriodValuePreFundedWarrantsExercised_e1ad37b1-6fd4-4250-9624-3cc3b76061fd" xlink:href="cris-20250630.xsd#cris_StockIssuedDuringPeriodValuePreFundedWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_cris_StockIssuedDuringPeriodValuePreFundedWarrantsExercised_e1ad37b1-6fd4-4250-9624-3cc3b76061fd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_4584ba40-b560-43f0-8b12-b138b00e775b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_4584ba40-b560-43f0-8b12-b138b00e775b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01b4a59b-7098-435b-83ad-dda0933e2dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_01b4a59b-7098-435b-83ad-dda0933e2dd3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesUnrealizedGainLoss_981140f8-2bb1-4b7a-a085-123bcdb84a26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_MarketableSecuritiesUnrealizedGainLoss_981140f8-2bb1-4b7a-a085-123bcdb84a26" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_5483c727-df6b-46c5-91d8-d53851c7008a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_9ceb102d-5a55-487d-94eb-0932a6529187" xlink:to="loc_us-gaap_NetIncomeLoss_5483c727-df6b-46c5-91d8-d53851c7008a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_53e25834-0455-48e8-91ba-d161997dd502" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_d8dc1e57-c75c-47c5-8fd0-a201d424f1af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/FairValueofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#FairValueofFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/FairValueofFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a00dbea4-7494-4e85-9dda-836a737f9ee9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_189835b8-e16b-4ec3-b9e6-63c87dc8a022" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a00dbea4-7494-4e85-9dda-836a737f9ee9" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_189835b8-e16b-4ec3-b9e6-63c87dc8a022" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_607d7102-089e-4679-9f91-0bdc3ac55243" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_189835b8-e16b-4ec3-b9e6-63c87dc8a022" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_607d7102-089e-4679-9f91-0bdc3ac55243" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_607d7102-089e-4679-9f91-0bdc3ac55243_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_607d7102-089e-4679-9f91-0bdc3ac55243" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_607d7102-089e-4679-9f91-0bdc3ac55243_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_00268929-6dc4-4f34-8de5-1282c7a1f124" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_607d7102-089e-4679-9f91-0bdc3ac55243" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_00268929-6dc4-4f34-8de5-1282c7a1f124" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_d935dfa6-a583-407e-9fb3-87055c3cdc07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_00268929-6dc4-4f34-8de5-1282c7a1f124" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_d935dfa6-a583-407e-9fb3-87055c3cdc07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44e26da3-6019-4e03-ac45-14165de635a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_189835b8-e16b-4ec3-b9e6-63c87dc8a022" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44e26da3-6019-4e03-ac45-14165de635a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_44e26da3-6019-4e03-ac45-14165de635a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44e26da3-6019-4e03-ac45-14165de635a5" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_44e26da3-6019-4e03-ac45-14165de635a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0c293862-7910-452b-a0a4-c91309b48df4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44e26da3-6019-4e03-ac45-14165de635a5" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0c293862-7910-452b-a0a4-c91309b48df4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_0dbc19cd-da8c-417b-8026-10f5e7e13f5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0c293862-7910-452b-a0a4-c91309b48df4" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_0dbc19cd-da8c-417b-8026-10f5e7e13f5f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_a9cf5f41-147e-4654-9cab-0b7190b6767d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0c293862-7910-452b-a0a4-c91309b48df4" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_a9cf5f41-147e-4654-9cab-0b7190b6767d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_4ebb9932-96c5-49c3-b24b-729fc60265cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0c293862-7910-452b-a0a4-c91309b48df4" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_4ebb9932-96c5-49c3-b24b-729fc60265cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_b485c036-83d7-4709-abba-6def54c5e04c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_189835b8-e16b-4ec3-b9e6-63c87dc8a022" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_b485c036-83d7-4709-abba-6def54c5e04c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_b485c036-83d7-4709-abba-6def54c5e04c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_b485c036-83d7-4709-abba-6def54c5e04c" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_b485c036-83d7-4709-abba-6def54c5e04c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e9d5729a-4453-4a41-8473-d5915e203b75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_b485c036-83d7-4709-abba-6def54c5e04c" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e9d5729a-4453-4a41-8473-d5915e203b75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_f4913d29-b8c3-4ed7-9c99-4770dadcde87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e9d5729a-4453-4a41-8473-d5915e203b75" xlink:to="loc_us-gaap_MoneyMarketFundsMember_f4913d29-b8c3-4ed7-9c99-4770dadcde87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAbstract_eb67c47f-03e3-4cd1-8a07-2bbea0aa4a93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a00dbea4-7494-4e85-9dda-836a737f9ee9" xlink:to="loc_us-gaap_CashAndCashEquivalentsAbstract_eb67c47f-03e3-4cd1-8a07-2bbea0aa4a93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_01b043ce-d660-469d-8b68-f3a7fe48b1f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAbstract_eb67c47f-03e3-4cd1-8a07-2bbea0aa4a93" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_01b043ce-d660-469d-8b68-f3a7fe48b1f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_88a55a48-8e86-4a46-a967-84d47c576abb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsAbstract_eb67c47f-03e3-4cd1-8a07-2bbea0aa4a93" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_88a55a48-8e86-4a46-a967-84d47c576abb" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/LiabilityRelatedtotheSaleofFutureRoyaltiesNarrativeDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#LiabilityRelatedtotheSaleofFutureRoyaltiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/LiabilityRelatedtotheSaleofFutureRoyaltiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonmonetaryTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonmonetaryTransactionByTypeTable_b387c3ce-ec60-4efd-bc2b-053be7947b5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonmonetaryTransactionByTypeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:to="loc_us-gaap_NonmonetaryTransactionByTypeTable_b387c3ce-ec60-4efd-bc2b-053be7947b5d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_2d5dd1d9-2c72-4e18-b080-76ab64bc2aa8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NonmonetaryTransactionByTypeTable_b387c3ce-ec60-4efd-bc2b-053be7947b5d" xlink:to="loc_srt_CounterpartyNameAxis_2d5dd1d9-2c72-4e18-b080-76ab64bc2aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2d5dd1d9-2c72-4e18-b080-76ab64bc2aa8_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_2d5dd1d9-2c72-4e18-b080-76ab64bc2aa8" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2d5dd1d9-2c72-4e18-b080-76ab64bc2aa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_fc17afd5-0963-4874-9e1d-04a45ef3a163" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_2d5dd1d9-2c72-4e18-b080-76ab64bc2aa8" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_fc17afd5-0963-4874-9e1d-04a45ef3a163" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_OberlandCapitalMember_1900212b-5ae9-4af8-bf23-d0ade972afb4" xlink:href="cris-20250630.xsd#cris_OberlandCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_fc17afd5-0963-4874-9e1d-04a45ef3a163" xlink:to="loc_cris_OberlandCapitalMember_1900212b-5ae9-4af8-bf23-d0ade972afb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ProceedsFromRoyaltyPurchaseAgreement_6a9556f8-5b56-4e37-9817-c9c23bd441ed" xlink:href="cris-20250630.xsd#cris_ProceedsFromRoyaltyPurchaseAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:to="loc_cris_ProceedsFromRoyaltyPurchaseAgreement_6a9556f8-5b56-4e37-9817-c9c23bd441ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_RoyaltyPurchaseAgreementTermsPurchaserDefaultOptionPeriod_8f02cbf2-5a01-4aa0-a1ee-f38a28e64cf2" xlink:href="cris-20250630.xsd#cris_RoyaltyPurchaseAgreementTermsPurchaserDefaultOptionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:to="loc_cris_RoyaltyPurchaseAgreementTermsPurchaserDefaultOptionPeriod_8f02cbf2-5a01-4aa0-a1ee-f38a28e64cf2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PercentageOfRoyaltyPurchaseAgreement_cb3ad304-c7e9-4bb3-b938-a640c9e83cf5" xlink:href="cris-20250630.xsd#cris_PercentageOfRoyaltyPurchaseAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:to="loc_cris_PercentageOfRoyaltyPurchaseAgreement_cb3ad304-c7e9-4bb3-b938-a640c9e83cf5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_RoyaltyPurchaseAgreementInterestRate_9350a274-a720-454a-a3cb-526c12599670" xlink:href="cris-20250630.xsd#cris_RoyaltyPurchaseAgreementInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:to="loc_cris_RoyaltyPurchaseAgreementInterestRate_9350a274-a720-454a-a3cb-526c12599670" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_RoyaltyPurchaseAgreementTransactionFeesAndClosingCosts_b0e77795-4689-4531-b59f-5219bb29c815" xlink:href="cris-20250630.xsd#cris_RoyaltyPurchaseAgreementTransactionFeesAndClosingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonmonetaryTransactionLineItems_7b130578-9e74-4c4f-b6a5-52442ed43e5f" xlink:to="loc_cris_RoyaltyPurchaseAgreementTransactionFeesAndClosingCosts_b0e77795-4689-4531-b59f-5219bb29c815" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/ResearchandDevelopmentCollaborationsDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#ResearchandDevelopmentCollaborationsDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/ResearchandDevelopmentCollaborationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_06463870-dfef-446a-aa7f-0cde8a6a2786" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_06463870-dfef-446a-aa7f-0cde8a6a2786" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_0703a829-0429-4d69-a138-886231e0a43b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_06463870-dfef-446a-aa7f-0cde8a6a2786" xlink:to="loc_srt_CounterpartyNameAxis_0703a829-0429-4d69-a138-886231e0a43b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0703a829-0429-4d69-a138-886231e0a43b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_0703a829-0429-4d69-a138-886231e0a43b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0703a829-0429-4d69-a138-886231e0a43b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8c9d39e7-ccfd-4431-a25b-1c724092b7cc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_0703a829-0429-4d69-a138-886231e0a43b" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8c9d39e7-ccfd-4431-a25b-1c724092b7cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_GenentechIncMember_8d9797a9-cf9a-471e-867d-897cd1d05484" xlink:href="cris-20250630.xsd#cris_GenentechIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8c9d39e7-ccfd-4431-a25b-1c724092b7cc" xlink:to="loc_cris_GenentechIncMember_8d9797a9-cf9a-471e-867d-897cd1d05484" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_AurigeneDiscoveryTechnologiesLtdMember_9f090076-94a7-4a5e-a2c9-34002bf2cd56" xlink:href="cris-20250630.xsd#cris_AurigeneDiscoveryTechnologiesLtdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_8c9d39e7-ccfd-4431-a25b-1c724092b7cc" xlink:to="loc_cris_AurigeneDiscoveryTechnologiesLtdMember_9f090076-94a7-4a5e-a2c9-34002bf2cd56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_3169175e-f276-46cd-86e4-f6bee52955d5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_06463870-dfef-446a-aa7f-0cde8a6a2786" xlink:to="loc_srt_RangeAxis_3169175e-f276-46cd-86e4-f6bee52955d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3169175e-f276-46cd-86e4-f6bee52955d5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_3169175e-f276-46cd-86e4-f6bee52955d5" xlink:to="loc_srt_RangeMember_3169175e-f276-46cd-86e4-f6bee52955d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_66905239-a21f-4e5f-8cda-c24187e255d2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_3169175e-f276-46cd-86e4-f6bee52955d5" xlink:to="loc_srt_RangeMember_66905239-a21f-4e5f-8cda-c24187e255d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_754b1439-af28-42b2-8d68-726931e548c9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_66905239-a21f-4e5f-8cda-c24187e255d2" xlink:to="loc_srt_MinimumMember_754b1439-af28-42b2-8d68-726931e548c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_1c75893e-b44f-4d3e-a906-688b0a843318" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_66905239-a21f-4e5f-8cda-c24187e255d2" xlink:to="loc_srt_MaximumMember_1c75893e-b44f-4d3e-a906-688b0a843318" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_97276c36-8d1e-4b4a-8ae8-ad79dd289a78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_06463870-dfef-446a-aa7f-0cde8a6a2786" xlink:to="loc_us-gaap_TypeOfArrangementAxis_97276c36-8d1e-4b4a-8ae8-ad79dd289a78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_97276c36-8d1e-4b4a-8ae8-ad79dd289a78_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_97276c36-8d1e-4b4a-8ae8-ad79dd289a78" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_97276c36-8d1e-4b4a-8ae8-ad79dd289a78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_3a6cc5e0-c70e-4951-9000-34f60426682e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_97276c36-8d1e-4b4a-8ae8-ad79dd289a78" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_3a6cc5e0-c70e-4951-9000-34f60426682e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_IRAK4PD1VISTAPD1TIM3ProgramMember_12ce7f25-39ac-4e6d-ab4c-414bf8a22248" xlink:href="cris-20250630.xsd#cris_IRAK4PD1VISTAPD1TIM3ProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_3a6cc5e0-c70e-4951-9000-34f60426682e" xlink:to="loc_cris_IRAK4PD1VISTAPD1TIM3ProgramMember_12ce7f25-39ac-4e6d-ab4c-414bf8a22248" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PercentageOfRoyaltyOnNetSales_ebee8720-ee7f-4586-9afd-c5488cdcb86a" xlink:href="cris-20250630.xsd#cris_PercentageOfRoyaltyOnNetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:to="loc_cris_PercentageOfRoyaltyOnNetSales_ebee8720-ee7f-4586-9afd-c5488cdcb86a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ReducedRoyaltyRate_42914945-ef73-41f7-a688-b49a4656445e" xlink:href="cris-20250630.xsd#cris_ReducedRoyaltyRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:to="loc_cris_ReducedRoyaltyRate_42914945-ef73-41f7-a688-b49a4656445e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_2e5585e3-87d8-447c-a0b9-04f89638cc11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_2e5585e3-87d8-447c-a0b9-04f89638cc11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_CollaborationAgreementTermsPercentageOfRoyaltyFeesReceivable_1d12ea67-24d4-4bb3-8fbf-4c2fdcc0def8" xlink:href="cris-20250630.xsd#cris_CollaborationAgreementTermsPercentageOfRoyaltyFeesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:to="loc_cris_CollaborationAgreementTermsPercentageOfRoyaltyFeesReceivable_1d12ea67-24d4-4bb3-8fbf-4c2fdcc0def8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationReceived1_76a227c5-41a8-4bcb-9132-963fedd5336f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationReceived1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_f30edfcc-eda7-4e24-9b5a-9e32d9058191" xlink:to="loc_us-gaap_OtherSignificantNoncashTransactionValueOfConsiderationReceived1_76a227c5-41a8-4bcb-9132-963fedd5336f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/StockholdersEquityDeficitNarrativeDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#StockholdersEquityDeficitNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/StockholdersEquityDeficitNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_01fad862-a3d3-4a52-88b7-e4ede9f2b8fa" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:to="loc_srt_CounterpartyNameAxis_01fad862-a3d3-4a52-88b7-e4ede9f2b8fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01fad862-a3d3-4a52-88b7-e4ede9f2b8fa_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_01fad862-a3d3-4a52-88b7-e4ede9f2b8fa" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_01fad862-a3d3-4a52-88b7-e4ede9f2b8fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_726e0ec8-d2eb-4532-9de1-882c35516f10" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_01fad862-a3d3-4a52-88b7-e4ede9f2b8fa" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_726e0ec8-d2eb-4532-9de1-882c35516f10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_CantorFitzgeraldAndCoMember_72f22773-66a1-4598-be84-e1d469aa7ff6" xlink:href="cris-20250630.xsd#cris_CantorFitzgeraldAndCoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_726e0ec8-d2eb-4532-9de1-882c35516f10" xlink:to="loc_cris_CantorFitzgeraldAndCoMember_72f22773-66a1-4598-be84-e1d469aa7ff6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_6e749f50-ac7a-428a-9c17-906a9c8179d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:to="loc_us-gaap_AwardTypeAxis_6e749f50-ac7a-428a-9c17-906a9c8179d1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e749f50-ac7a-428a-9c17-906a9c8179d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6e749f50-ac7a-428a-9c17-906a9c8179d1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e749f50-ac7a-428a-9c17-906a9c8179d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_24d90f24-da25-4b98-8490-bb9b5081e305" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6e749f50-ac7a-428a-9c17-906a9c8179d1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_24d90f24-da25-4b98-8490-bb9b5081e305" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_f32fd381-fa4b-48d6-8ca2-15629dfff16e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_24d90f24-da25-4b98-8490-bb9b5081e305" xlink:to="loc_us-gaap_CommonStockMember_f32fd381-fa4b-48d6-8ca2-15629dfff16e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_7642c26c-cce0-4c15-afb3-aa67b390a530" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_7642c26c-cce0-4c15-afb3-aa67b390a530" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7642c26c-cce0-4c15-afb3-aa67b390a530_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_7642c26c-cce0-4c15-afb3-aa67b390a530" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7642c26c-cce0-4c15-afb3-aa67b390a530_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_7642c26c-cce0-4c15-afb3-aa67b390a530" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_87a85d3d-ebd3-413d-9178-52f43525b734" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:to="loc_us-gaap_PrivatePlacementMember_87a85d3d-ebd3-413d-9178-52f43525b734" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_October2024OfferingsMember_a3b6e93e-3165-4652-befd-ca477ccacd49" xlink:href="cris-20250630.xsd#cris_October2024OfferingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:to="loc_cris_October2024OfferingsMember_a3b6e93e-3165-4652-befd-ca477ccacd49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_March2025OfferingsMember_e2a73e8b-71fe-43d6-955d-4f4d14287430" xlink:href="cris-20250630.xsd#cris_March2025OfferingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:to="loc_cris_March2025OfferingsMember_e2a73e8b-71fe-43d6-955d-4f4d14287430" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_RegisteredDirectOfferingMember_ab80643a-af50-4f24-835a-b7a477f4bee7" xlink:href="cris-20250630.xsd#cris_RegisteredDirectOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:to="loc_cris_RegisteredDirectOfferingMember_ab80643a-af50-4f24-835a-b7a477f4bee7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_July2025OfferingsMember_d5be859e-75bd-4183-8df0-227bee42a433" xlink:href="cris-20250630.xsd#cris_July2025OfferingsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_91a937ef-98e8-4272-ae5b-8bf08b42059b" xlink:to="loc_cris_July2025OfferingsMember_d5be859e-75bd-4183-8df0-227bee42a433" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_040aeff0-52d1-44bb-b419-fff8ca2a04d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_040aeff0-52d1-44bb-b419-fff8ca2a04d3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_040aeff0-52d1-44bb-b419-fff8ca2a04d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_040aeff0-52d1-44bb-b419-fff8ca2a04d3" xlink:to="loc_us-gaap_EquityComponentDomain_040aeff0-52d1-44bb-b419-fff8ca2a04d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b937a86b-eeaf-4874-82fd-3c6c3b6aa207" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_040aeff0-52d1-44bb-b419-fff8ca2a04d3" xlink:to="loc_us-gaap_EquityComponentDomain_b937a86b-eeaf-4874-82fd-3c6c3b6aa207" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_abaa26f7-fc7a-4f62-9d57-106bf1954244" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b937a86b-eeaf-4874-82fd-3c6c3b6aa207" xlink:to="loc_us-gaap_CommonStockMember_abaa26f7-fc7a-4f62-9d57-106bf1954244" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_ae1d82b2-b616-4ce5-8666-4f3c884d7dea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_ae1d82b2-b616-4ce5-8666-4f3c884d7dea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_ae1d82b2-b616-4ce5-8666-4f3c884d7dea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_ae1d82b2-b616-4ce5-8666-4f3c884d7dea" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_ae1d82b2-b616-4ce5-8666-4f3c884d7dea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_0683c7a0-57bf-4d15-bce3-aa2b0393d999" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_ae1d82b2-b616-4ce5-8666-4f3c884d7dea" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_0683c7a0-57bf-4d15-bce3-aa2b0393d999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_UnregisteredWarrantsMember_7d5670da-6165-475a-b554-277f353c07de" xlink:href="cris-20250630.xsd#cris_UnregisteredWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_0683c7a0-57bf-4d15-bce3-aa2b0393d999" xlink:to="loc_cris_UnregisteredWarrantsMember_7d5670da-6165-475a-b554-277f353c07de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PreFundedUnregisteredWarrantsMember_a0ad63f8-3c5d-4006-a646-db9da90a374d" xlink:href="cris-20250630.xsd#cris_PreFundedUnregisteredWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_0683c7a0-57bf-4d15-bce3-aa2b0393d999" xlink:to="loc_cris_PreFundedUnregisteredWarrantsMember_a0ad63f8-3c5d-4006-a646-db9da90a374d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PreFundedWarrantsMember_f175a169-5442-49ba-a2d4-d6a06041eb25" xlink:href="cris-20250630.xsd#cris_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_0683c7a0-57bf-4d15-bce3-aa2b0393d999" xlink:to="loc_cris_PreFundedWarrantsMember_f175a169-5442-49ba-a2d4-d6a06041eb25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_c271f323-fb07-46de-80d7-ce4f1ab0984b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_61d29cb8-00c9-41ed-a9d8-0ee3ec94e995" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_c271f323-fb07-46de-80d7-ce4f1ab0984b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_c271f323-fb07-46de-80d7-ce4f1ab0984b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_c271f323-fb07-46de-80d7-ce4f1ab0984b" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_c271f323-fb07-46de-80d7-ce4f1ab0984b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_09c601fe-0ac7-4902-87b3-98fc14ebfe4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_c271f323-fb07-46de-80d7-ce4f1ab0984b" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_09c601fe-0ac7-4902-87b3-98fc14ebfe4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_c3b286dc-8657-44a4-9940-08422518511e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_09c601fe-0ac7-4902-87b3-98fc14ebfe4f" xlink:to="loc_us-gaap_SubsequentEventMember_c3b286dc-8657-44a4-9940-08422518511e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_984b98ad-9cd9-4647-86f8-c685b47bf72c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_984b98ad-9cd9-4647-86f8-c685b47bf72c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_SaleOfStockAuthorizedMaximumAmount_3132254d-efec-48fb-b38c-ec2e98902a92" xlink:href="cris-20250630.xsd#cris_SaleOfStockAuthorizedMaximumAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_SaleOfStockAuthorizedMaximumAmount_3132254d-efec-48fb-b38c-ec2e98902a92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockSaleAgreementCompensationFeePercentageOfGrossProceeds_fb1f9b29-aab2-40c8-8e5d-baf91715e280" xlink:href="cris-20250630.xsd#cris_StockSaleAgreementCompensationFeePercentageOfGrossProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_StockSaleAgreementCompensationFeePercentageOfGrossProceeds_fb1f9b29-aab2-40c8-8e5d-baf91715e280" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_11e9c8e9-a958-4bca-a1a4-2047b12d56ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_11e9c8e9-a958-4bca-a1a4-2047b12d56ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockSaleAgreementRemainingAuthorizedAmount_5179af89-0e98-48a8-8843-154f1d61e762" xlink:href="cris-20250630.xsd#cris_StockSaleAgreementRemainingAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_StockSaleAgreementRemainingAuthorizedAmount_5179af89-0e98-48a8-8843-154f1d61e762" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockSaleAgreementSaleRestrictionMaximumPublicFloat_55f529c8-bde9-4fcf-9aa1-6761a5157407" xlink:href="cris-20250630.xsd#cris_StockSaleAgreementSaleRestrictionMaximumPublicFloat"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_StockSaleAgreementSaleRestrictionMaximumPublicFloat_55f529c8-bde9-4fcf-9aa1-6761a5157407" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_SaleOfStockAgreementMaximumPercentageOfPublicFloat_c1df6dc7-84a4-474c-8863-9ad7fe0492e8" xlink:href="cris-20250630.xsd#cris_SaleOfStockAgreementMaximumPercentageOfPublicFloat"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_SaleOfStockAgreementMaximumPercentageOfPublicFloat_c1df6dc7-84a4-474c-8863-9ad7fe0492e8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockSaleAgreementSaleRestrictionPeriod_0070f9f8-16f6-4bf6-bfe7-21f48368df14" xlink:href="cris-20250630.xsd#cris_StockSaleAgreementSaleRestrictionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_StockSaleAgreementSaleRestrictionPeriod_0070f9f8-16f6-4bf6-bfe7-21f48368df14" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_2fd0422b-255d-4a8e-9313-e103b28a6745" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_2fd0422b-255d-4a8e-9313-e103b28a6745" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_756294bf-b64f-49f7-b935-f0f14e46c8bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_756294bf-b64f-49f7-b935-f0f14e46c8bd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ClassOfWarrantOrRightExpirationPeriod_fcd2eee4-8cbd-49ce-9948-de05255001c3" xlink:href="cris-20250630.xsd#cris_ClassOfWarrantOrRightExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_ClassOfWarrantOrRightExpirationPeriod_fcd2eee4-8cbd-49ce-9948-de05255001c3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PurchasePriceShare_07c639e3-3ce9-436a-b58b-7ea5eb0219d9" xlink:href="cris-20250630.xsd#cris_PurchasePriceShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_PurchasePriceShare_07c639e3-3ce9-436a-b58b-7ea5eb0219d9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_SaleOfEquityPricePerShare_1bf8909a-18f8-4313-9046-5e6c9cc295b5" xlink:href="cris-20250630.xsd#cris_SaleOfEquityPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_SaleOfEquityPricePerShare_1bf8909a-18f8-4313-9046-5e6c9cc295b5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_SaleOfEquityConsiderationReceivedOnTransaction_fab11ed3-65ad-47a4-9fd4-3163f71c0c4d" xlink:href="cris-20250630.xsd#cris_SaleOfEquityConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_SaleOfEquityConsiderationReceivedOnTransaction_fab11ed3-65ad-47a4-9fd4-3163f71c0c4d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockIssuedDuringPeriodCommonStockFairValue_ed458c86-480e-4d41-b3c6-72d4afadc28b" xlink:href="cris-20250630.xsd#cris_StockIssuedDuringPeriodCommonStockFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_StockIssuedDuringPeriodCommonStockFairValue_ed458c86-480e-4d41-b3c6-72d4afadc28b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_ef10c028-38fc-4325-8359-0ad6c7f0b48c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantsNotSettleableInCashFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_us-gaap_WarrantsNotSettleableInCashFairValueDisclosure_ef10c028-38fc-4325-8359-0ad6c7f0b48c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ClassOfWarrantOrRightPurchasePrice_8fb0c2cf-e8d4-45da-9d76-e3d24303240e" xlink:href="cris-20250630.xsd#cris_ClassOfWarrantOrRightPurchasePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_3c703fe7-b0a1-4f44-a3e0-9f429305a886" xlink:to="loc_cris_ClassOfWarrantOrRightPurchasePrice_8fb0c2cf-e8d4-45da-9d76-e3d24303240e" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/StockholdersEquityDeficitScheduleoftheWarrantsUsingtheBlackScholesOptionPricingModelwiththeFollowingWeightedAverageInputsDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#StockholdersEquityDeficitScheduleoftheWarrantsUsingtheBlackScholesOptionPricingModelwiththeFollowingWeightedAverageInputsDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/StockholdersEquityDeficitScheduleoftheWarrantsUsingtheBlackScholesOptionPricingModelwiththeFollowingWeightedAverageInputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_f7e22765-9599-4e8c-80d1-96d30f3f100c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_d7e067d6-8ce2-4c9e-9248-d38b2c0d44fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_f7e22765-9599-4e8c-80d1-96d30f3f100c" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_d7e067d6-8ce2-4c9e-9248-d38b2c0d44fa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_c2ba9e09-514f-49bf-ad16-1f6689d9b0ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_d7e067d6-8ce2-4c9e-9248-d38b2c0d44fa" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_c2ba9e09-514f-49bf-ad16-1f6689d9b0ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_c2ba9e09-514f-49bf-ad16-1f6689d9b0ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_c2ba9e09-514f-49bf-ad16-1f6689d9b0ea" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_c2ba9e09-514f-49bf-ad16-1f6689d9b0ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_c2ba9e09-514f-49bf-ad16-1f6689d9b0ea" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_2f34aa0c-149f-47c6-9845-0fd0a41890a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_2f34aa0c-149f-47c6-9845-0fd0a41890a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_cb5d4db3-302e-4805-bd25-ea42823a88bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_cb5d4db3-302e-4805-bd25-ea42823a88bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_ccb9533b-2e20-44bc-96c1-227a4841974c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_ccb9533b-2e20-44bc-96c1-227a4841974c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputOptionVolatilityMember_042c616e-51e5-4c7f-bb63-c91d68bfc18b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputOptionVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:to="loc_us-gaap_MeasurementInputOptionVolatilityMember_042c616e-51e5-4c7f-bb63-c91d68bfc18b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedDividendRateMember_50c4bc4d-194a-4d4a-a434-8895dabf0a69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedDividendRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_b7e996e8-e61d-42c7-8298-194483ced277" xlink:to="loc_us-gaap_MeasurementInputExpectedDividendRateMember_50c4bc4d-194a-4d4a-a434-8895dabf0a69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_b31c4d7d-10ce-4a10-b334-cbb7a25866c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_d7e067d6-8ce2-4c9e-9248-d38b2c0d44fa" xlink:to="loc_us-gaap_ValuationTechniqueAxis_b31c4d7d-10ce-4a10-b334-cbb7a25866c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_b31c4d7d-10ce-4a10-b334-cbb7a25866c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_b31c4d7d-10ce-4a10-b334-cbb7a25866c2" xlink:to="loc_us-gaap_ValuationTechniqueDomain_b31c4d7d-10ce-4a10-b334-cbb7a25866c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_42674f6b-228d-49c9-aac4-59b7f4cfe5a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_b31c4d7d-10ce-4a10-b334-cbb7a25866c2" xlink:to="loc_us-gaap_ValuationTechniqueDomain_42674f6b-228d-49c9-aac4-59b7f4cfe5a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueOptionPricingModelMember_a7841536-2ad0-45cd-94f6-4d0dc68c1d6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_42674f6b-228d-49c9-aac4-59b7f4cfe5a8" xlink:to="loc_us-gaap_ValuationTechniqueOptionPricingModelMember_a7841536-2ad0-45cd-94f6-4d0dc68c1d6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_73d28687-89c1-4a73-ac73-f0b4c6902f02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f7e22765-9599-4e8c-80d1-96d30f3f100c" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_73d28687-89c1-4a73-ac73-f0b4c6902f02" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/StockPlansandStockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#StockPlansandStockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/StockPlansandStockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_afdd4009-a225-438b-af48-df30b3e26137" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_afdd4009-a225-438b-af48-df30b3e26137" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_a860c5bd-3931-47ed-9c6e-07a0e1ee7a02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_afdd4009-a225-438b-af48-df30b3e26137" xlink:to="loc_us-gaap_AwardTypeAxis_a860c5bd-3931-47ed-9c6e-07a0e1ee7a02" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a860c5bd-3931-47ed-9c6e-07a0e1ee7a02_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_a860c5bd-3931-47ed-9c6e-07a0e1ee7a02" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a860c5bd-3931-47ed-9c6e-07a0e1ee7a02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_a860c5bd-3931-47ed-9c6e-07a0e1ee7a02" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_cf7ca2dc-04c7-4b8e-b65a-646dd28c7fcb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:to="loc_us-gaap_EmployeeStockOptionMember_cf7ca2dc-04c7-4b8e-b65a-646dd28c7fcb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockOptionsorStockAppreciationRightsMember_b8ca3614-dd7b-479e-b58e-2649bbde378a" xlink:href="cris-20250630.xsd#cris_StockOptionsorStockAppreciationRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:to="loc_cris_StockOptionsorStockAppreciationRightsMember_b8ca3614-dd7b-479e-b58e-2649bbde378a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_RestrictedStockRSUsOtherStockBasedAwardsOrPerformanceAwardsMember_bad08905-6bf6-45cc-b300-7c833d860dbb" xlink:href="cris-20250630.xsd#cris_RestrictedStockRSUsOtherStockBasedAwardsOrPerformanceAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:to="loc_cris_RestrictedStockRSUsOtherStockBasedAwardsOrPerformanceAwardsMember_bad08905-6bf6-45cc-b300-7c833d860dbb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_5aa0772b-1d5f-4552-9057-e82115b44cab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_5aa0772b-1d5f-4552-9057-e82115b44cab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_720e80e5-9ab5-4dc9-b5b3-865de6fce623" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9b3c2c36-a635-4d13-b818-5d4df32382ac" xlink:to="loc_us-gaap_EmployeeStockMember_720e80e5-9ab5-4dc9-b5b3-865de6fce623" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_95168420-57c5-4c2e-8748-e734d1b6ffbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_afdd4009-a225-438b-af48-df30b3e26137" xlink:to="loc_us-gaap_PlanNameAxis_95168420-57c5-4c2e-8748-e734d1b6ffbb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_95168420-57c5-4c2e-8748-e734d1b6ffbb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_95168420-57c5-4c2e-8748-e734d1b6ffbb" xlink:to="loc_us-gaap_PlanNameDomain_95168420-57c5-4c2e-8748-e734d1b6ffbb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_19cffa9b-fbed-4b54-b5f4-42da59e5e88d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_95168420-57c5-4c2e-8748-e734d1b6ffbb" xlink:to="loc_us-gaap_PlanNameDomain_19cffa9b-fbed-4b54-b5f4-42da59e5e88d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_AmendedAndRestatedTwoThousandTenStockIncentivePlanMember_9c23802d-dd31-42a1-9f8d-1cd66974a352" xlink:href="cris-20250630.xsd#cris_AmendedAndRestatedTwoThousandTenStockIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_19cffa9b-fbed-4b54-b5f4-42da59e5e88d" xlink:to="loc_cris_AmendedAndRestatedTwoThousandTenStockIncentivePlanMember_9c23802d-dd31-42a1-9f8d-1cd66974a352" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_TwoThousandAndTenPlanMember_fc48a63e-767a-45f1-921c-0980ec6e0258" xlink:href="cris-20250630.xsd#cris_TwoThousandAndTenPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_19cffa9b-fbed-4b54-b5f4-42da59e5e88d" xlink:to="loc_cris_TwoThousandAndTenPlanMember_fc48a63e-767a-45f1-921c-0980ec6e0258" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_EmployeeStockPurchasePlanMember_ed5c3aeb-0eb1-4046-b916-891766428940" xlink:href="cris-20250630.xsd#cris_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_19cffa9b-fbed-4b54-b5f4-42da59e5e88d" xlink:to="loc_cris_EmployeeStockPurchasePlanMember_ed5c3aeb-0eb1-4046-b916-891766428940" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_dbfe6169-ffff-4036-a2ee-394d1063e882" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_afdd4009-a225-438b-af48-df30b3e26137" xlink:to="loc_us-gaap_VestingAxis_dbfe6169-ffff-4036-a2ee-394d1063e882" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_dbfe6169-ffff-4036-a2ee-394d1063e882_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_dbfe6169-ffff-4036-a2ee-394d1063e882" xlink:to="loc_us-gaap_VestingDomain_dbfe6169-ffff-4036-a2ee-394d1063e882_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_5e624036-6a06-4108-a173-e6fa6ed1d69b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_dbfe6169-ffff-4036-a2ee-394d1063e882" xlink:to="loc_us-gaap_VestingDomain_5e624036-6a06-4108-a173-e6fa6ed1d69b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_04bb797f-9c05-4ca7-bfbe-3154dd226697" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_5e624036-6a06-4108-a173-e6fa6ed1d69b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_04bb797f-9c05-4ca7-bfbe-3154dd226697" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_eedde2e9-4d68-4fd2-ba0f-36a15f05963b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_5e624036-6a06-4108-a173-e6fa6ed1d69b" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_eedde2e9-4d68-4fd2-ba0f-36a15f05963b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_42e2ee0d-cd2c-417f-807a-672ea46ee60a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_afdd4009-a225-438b-af48-df30b3e26137" xlink:to="loc_srt_TitleOfIndividualAxis_42e2ee0d-cd2c-417f-807a-672ea46ee60a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_42e2ee0d-cd2c-417f-807a-672ea46ee60a_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_42e2ee0d-cd2c-417f-807a-672ea46ee60a" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_42e2ee0d-cd2c-417f-807a-672ea46ee60a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_94c65689-2cb4-4a3e-99ae-eafceadf2330" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_42e2ee0d-cd2c-417f-807a-672ea46ee60a" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_94c65689-2cb4-4a3e-99ae-eafceadf2330" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_NonEmployeeDirectorsMember_a88b3469-125c-40b1-9b7e-542e0d239de8" xlink:href="cris-20250630.xsd#cris_NonEmployeeDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_94c65689-2cb4-4a3e-99ae-eafceadf2330" xlink:to="loc_cris_NonEmployeeDirectorsMember_a88b3469-125c-40b1-9b7e-542e0d239de8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ShareBasedCompensationPlans_59b76b16-90f9-4a7f-a878-fc290b13585f" xlink:href="cris-20250630.xsd#cris_ShareBasedCompensationPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_ShareBasedCompensationPlans_59b76b16-90f9-4a7f-a878-fc290b13585f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_CommonStockAdditionalCapitalSharesReservedForFutureIssuance_fa6345e4-c6ba-428a-956d-273b19943502" xlink:href="cris-20250630.xsd#cris_CommonStockAdditionalCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_CommonStockAdditionalCapitalSharesReservedForFutureIssuance_fa6345e4-c6ba-428a-956d-273b19943502" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_6709ae8e-1dd0-42c2-9b39-92e0cf7c492e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_6709ae8e-1dd0-42c2-9b39-92e0cf7c492e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_af044f75-8409-45b4-ac5c-a934adca8da0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_af044f75-8409-45b4-ac5c-a934adca8da0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesRemovedFromAvailableSharePoolPerShare_5aa2a22b-a15c-4955-89bd-d79622c32700" xlink:href="cris-20250630.xsd#cris_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesRemovedFromAvailableSharePoolPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesRemovedFromAvailableSharePoolPerShare_5aa2a22b-a15c-4955-89bd-d79622c32700" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_e065a06d-fa72-4143-a262-85abac3db2db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_e065a06d-fa72-4143-a262-85abac3db2db" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_NumberOfSharesAwardedUnderStockValueLessThanSpecificPercentageOfFairMarketValue_8fb06782-824b-425d-b57e-60aaec580fc4" xlink:href="cris-20250630.xsd#cris_NumberOfSharesAwardedUnderStockValueLessThanSpecificPercentageOfFairMarketValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_NumberOfSharesAwardedUnderStockValueLessThanSpecificPercentageOfFairMarketValue_8fb06782-824b-425d-b57e-60aaec580fc4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_ea6140dd-8191-446a-8c1c-f5743d48d83e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_ea6140dd-8191-446a-8c1c-f5743d48d83e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_d89a681c-b3b8-47e6-9717-33004e992878" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_d89a681c-b3b8-47e6-9717-33004e992878" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_9e08debf-4a14-4a9c-8ef0-7504a6b4b064" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_9e08debf-4a14-4a9c-8ef0-7504a6b4b064" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3509288a-f9fd-41a0-b810-271c9ea15787" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3509288a-f9fd-41a0-b810-271c9ea15787" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5b0c6234-d32a-4382-987f-5c917db1a29b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5b0c6234-d32a-4382-987f-5c917db1a29b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_2dfa30e9-d873-4b26-919b-eb5b9c862eaa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_2dfa30e9-d873-4b26-919b-eb5b9c862eaa" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_25907260-cac9-43c7-a91b-9b0346e2bde9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_25907260-cac9-43c7-a91b-9b0346e2bde9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_e52137ca-372f-4a18-8cfc-f92ad3e8abf9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_e52137ca-372f-4a18-8cfc-f92ad3e8abf9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_cadb5d1b-c4a2-4577-b051-d4701af9eb7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_cadb5d1b-c4a2-4577-b051-d4701af9eb7c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_EmployeeStockPurchasePlanEnrollmentPeriod_3dc03f09-c19e-472f-a7f5-c58412a7f871" xlink:href="cris-20250630.xsd#cris_EmployeeStockPurchasePlanEnrollmentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_EmployeeStockPurchasePlanEnrollmentPeriod_3dc03f09-c19e-472f-a7f5-c58412a7f871" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_NumberOfPurchasePeriodsPerEnrollmentPeriod_1bbea3f3-0e3a-4e01-8bbd-1a863fd8e22f" xlink:href="cris-20250630.xsd#cris_NumberOfPurchasePeriodsPerEnrollmentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_NumberOfPurchasePeriodsPerEnrollmentPeriod_1bbea3f3-0e3a-4e01-8bbd-1a863fd8e22f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_SharebasedCompensationArrangementBySharebasedPaymentAwardStockPlanOfferingPeriod_84358156-29cd-40c9-874c-1227cf749c7f" xlink:href="cris-20250630.xsd#cris_SharebasedCompensationArrangementBySharebasedPaymentAwardStockPlanOfferingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_SharebasedCompensationArrangementBySharebasedPaymentAwardStockPlanOfferingPeriod_84358156-29cd-40c9-874c-1227cf749c7f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_74616e41-dabe-4e2f-93a4-e3e368d86f02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_74616e41-dabe-4e2f-93a4-e3e368d86f02" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_StockAvailableForFuturePurchaseUnderEmployeeStockPurchasePlans_bded261b-7c5d-416f-89b4-2f3390ec6441" xlink:href="cris-20250630.xsd#cris_StockAvailableForFuturePurchaseUnderEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5d95fb31-3ab2-4970-b740-4d699f6cf908" xlink:to="loc_cris_StockAvailableForFuturePurchaseUnderEmployeeStockPurchasePlans_bded261b-7c5d-416f-89b4-2f3390ec6441" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/StockPlansandStockBasedCompensationScheduleofValuationAssumptionsUsedtoCalculateFairValueofEmployeeOptionsAwardedDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#StockPlansandStockBasedCompensationScheduleofValuationAssumptionsUsedtoCalculateFairValueofEmployeeOptionsAwardedDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/StockPlansandStockBasedCompensationScheduleofValuationAssumptionsUsedtoCalculateFairValueofEmployeeOptionsAwardedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_c9170ca4-9236-42d2-afba-4f6c593a95d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_c9170ca4-9236-42d2-afba-4f6c593a95d9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b1e6aac6-9028-4194-a1af-7c1319aef0f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_c9170ca4-9236-42d2-afba-4f6c593a95d9" xlink:to="loc_us-gaap_AwardTypeAxis_b1e6aac6-9028-4194-a1af-7c1319aef0f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b1e6aac6-9028-4194-a1af-7c1319aef0f6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b1e6aac6-9028-4194-a1af-7c1319aef0f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b1e6aac6-9028-4194-a1af-7c1319aef0f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c5508653-6bc8-422a-a739-f462ac162194" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b1e6aac6-9028-4194-a1af-7c1319aef0f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c5508653-6bc8-422a-a739-f462ac162194" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_13209ee7-8283-4ba4-989f-f3643b2af04c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c5508653-6bc8-422a-a739-f462ac162194" xlink:to="loc_us-gaap_EmployeeStockOptionMember_13209ee7-8283-4ba4-989f-f3643b2af04c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_38cc94e7-5e37-46e3-ab84-6729877cf664" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_38cc94e7-5e37-46e3-ab84-6729877cf664" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_132db706-e3ab-410d-b93f-55a73b8e7839" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_132db706-e3ab-410d-b93f-55a73b8e7839" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_49649fdf-05b4-416a-9176-2f9934cec3dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_49649fdf-05b4-416a-9176-2f9934cec3dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_ffb753ea-c440-4ed0-bdc7-3336ca628bda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_ffb753ea-c440-4ed0-bdc7-3336ca628bda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_6d88fcd6-b5eb-4b39-8684-43195c5f5cfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_6d88fcd6-b5eb-4b39-8684-43195c5f5cfc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_e2e18650-15c5-4f64-8cf4-94b036cb0e0c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_5803949f-1287-4284-895e-93ab065e58a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_e2e18650-15c5-4f64-8cf4-94b036cb0e0c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/StockPlansandStockBasedCompensationScheduleofRestrictedStockAwardsDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#StockPlansandStockBasedCompensationScheduleofRestrictedStockAwardsDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/StockPlansandStockBasedCompensationScheduleofRestrictedStockAwardsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c99d0cc4-dbbc-476e-9df6-b8fe9c969a11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6cdfdde3-a5ca-4f45-879e-8aedf273027a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c99d0cc4-dbbc-476e-9df6-b8fe9c969a11" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6cdfdde3-a5ca-4f45-879e-8aedf273027a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_a0667723-87b4-4eae-889c-9b2494221fb9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6cdfdde3-a5ca-4f45-879e-8aedf273027a" xlink:to="loc_us-gaap_AwardTypeAxis_a0667723-87b4-4eae-889c-9b2494221fb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0667723-87b4-4eae-889c-9b2494221fb9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_a0667723-87b4-4eae-889c-9b2494221fb9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0667723-87b4-4eae-889c-9b2494221fb9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54fd339b-3afc-48af-bce6-2ac8d352b33c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_a0667723-87b4-4eae-889c-9b2494221fb9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54fd339b-3afc-48af-bce6-2ac8d352b33c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_cceae19f-4093-4bad-9a21-ffd5b9b29dd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54fd339b-3afc-48af-bce6-2ac8d352b33c" xlink:to="loc_us-gaap_RestrictedStockMember_cceae19f-4093-4bad-9a21-ffd5b9b29dd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_889c231d-e080-43e2-a344-df80a66971f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54fd339b-3afc-48af-bce6-2ac8d352b33c" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_889c231d-e080-43e2-a344-df80a66971f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_c32ef174-91f3-4101-b983-982d26cb645d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6cdfdde3-a5ca-4f45-879e-8aedf273027a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_c32ef174-91f3-4101-b983-982d26cb645d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c32ef174-91f3-4101-b983-982d26cb645d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_c32ef174-91f3-4101-b983-982d26cb645d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_c32ef174-91f3-4101-b983-982d26cb645d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_539daf7e-1e64-482e-a376-63bace256154" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_c32ef174-91f3-4101-b983-982d26cb645d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_539daf7e-1e64-482e-a376-63bace256154" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_fcd743b2-6c94-4d99-a310-5dfafc5a25ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_539daf7e-1e64-482e-a376-63bace256154" xlink:to="loc_us-gaap_EmployeeStockOptionMember_fcd743b2-6c94-4d99-a310-5dfafc5a25ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_09cb471b-88b7-4ada-b17d-7133914f6e40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_539daf7e-1e64-482e-a376-63bace256154" xlink:to="loc_us-gaap_RestrictedStockMember_09cb471b-88b7-4ada-b17d-7133914f6e40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_6003851f-486f-4c20-bef9-cf6339d3311b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_539daf7e-1e64-482e-a376-63bace256154" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_6003851f-486f-4c20-bef9-cf6339d3311b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_3c8c74a3-1f67-4a51-b867-c160cd628d49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c99d0cc4-dbbc-476e-9df6-b8fe9c969a11" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_3c8c74a3-1f67-4a51-b867-c160cd628d49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_3bbcd8a8-9f42-4cd2-ab99-04a655661565" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_3c8c74a3-1f67-4a51-b867-c160cd628d49" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_3bbcd8a8-9f42-4cd2-ab99-04a655661565" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_88055efa-975b-495a-a0c4-3132570af77d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_3c8c74a3-1f67-4a51-b867-c160cd628d49" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_88055efa-975b-495a-a0c4-3132570af77d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_fb5fa8cd-33e6-48de-b9ba-9e07d3318125" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_3c8c74a3-1f67-4a51-b867-c160cd628d49" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_fb5fa8cd-33e6-48de-b9ba-9e07d3318125" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_1f5105ad-5556-4cd5-bd80-f4bcc2cbe9de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_3c8c74a3-1f67-4a51-b867-c160cd628d49" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_1f5105ad-5556-4cd5-bd80-f4bcc2cbe9de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_e7107195-1670-4800-a138-485de04cb4e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_46f21914-17a0-4cf6-b1c3-505a02ba0f60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c99d0cc4-dbbc-476e-9df6-b8fe9c969a11" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_46f21914-17a0-4cf6-b1c3-505a02ba0f60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_9ce1260b-e57d-4db8-9c37-a6868422f385" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_46f21914-17a0-4cf6-b1c3-505a02ba0f60" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_9ce1260b-e57d-4db8-9c37-a6868422f385" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_af3860ef-9d47-41c5-81e9-3caeaa31fdd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_46f21914-17a0-4cf6-b1c3-505a02ba0f60" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_af3860ef-9d47-41c5-81e9-3caeaa31fdd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_814d2368-a329-4435-b564-27a63c3af24e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_46f21914-17a0-4cf6-b1c3-505a02ba0f60" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_814d2368-a329-4435-b564-27a63c3af24e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_3dd4e12b-f8da-498f-a127-ecac0fb8001e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_46f21914-17a0-4cf6-b1c3-505a02ba0f60" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_3dd4e12b-f8da-498f-a127-ecac0fb8001e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_cc31d786-043c-49e8-b3a3-14a37d9059a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/StockPlansandStockBasedCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#StockPlansandStockBasedCompensationScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/StockPlansandStockBasedCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_db439ef1-8563-4849-bf87-6d06006b919e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_49c9174b-b6cb-4742-9777-570780e9a7fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_db439ef1-8563-4849-bf87-6d06006b919e" xlink:to="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_49c9174b-b6cb-4742-9777-570780e9a7fe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_d99d2245-5848-4e51-8a27-a8bc58fc548c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDeferredCompensationArrangementWithIndividualShareBasedPaymentsTable_49c9174b-b6cb-4742-9777-570780e9a7fe" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_d99d2245-5848-4e51-8a27-a8bc58fc548c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d99d2245-5848-4e51-8a27-a8bc58fc548c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d99d2245-5848-4e51-8a27-a8bc58fc548c" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d99d2245-5848-4e51-8a27-a8bc58fc548c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_eb5bfc7a-931c-4d77-8a59-f36bd69047f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d99d2245-5848-4e51-8a27-a8bc58fc548c" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_eb5bfc7a-931c-4d77-8a59-f36bd69047f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_84e2ace0-7811-4d19-a9e7-1984fa9e821c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_eb5bfc7a-931c-4d77-8a59-f36bd69047f8" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_84e2ace0-7811-4d19-a9e7-1984fa9e821c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_a11ec08d-eb31-495b-9d95-6d33e66242f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_eb5bfc7a-931c-4d77-8a59-f36bd69047f8" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_a11ec08d-eb31-495b-9d95-6d33e66242f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_79b2b01b-2768-4d45-9f09-c4ec790a1559" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsLineItems_db439ef1-8563-4849-bf87-6d06006b919e" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_79b2b01b-2768-4d45-9f09-c4ec790a1559" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/LossPerCommonShareNarrativeDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#LossPerCommonShareNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/LossPerCommonShareNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_383b741e-d38e-45a0-b212-ad0eec82eaa5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_4932890e-7ac3-4ad4-8f0c-9a99776d080a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_383b741e-d38e-45a0-b212-ad0eec82eaa5" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_4932890e-7ac3-4ad4-8f0c-9a99776d080a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d50e4f4f-4dfb-4f37-a9bf-b66baee8124d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_4932890e-7ac3-4ad4-8f0c-9a99776d080a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d50e4f4f-4dfb-4f37-a9bf-b66baee8124d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d50e4f4f-4dfb-4f37-a9bf-b66baee8124d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d50e4f4f-4dfb-4f37-a9bf-b66baee8124d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d50e4f4f-4dfb-4f37-a9bf-b66baee8124d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e0a08e66-ae5a-498a-a259-005fba238f85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d50e4f4f-4dfb-4f37-a9bf-b66baee8124d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e0a08e66-ae5a-498a-a259-005fba238f85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_PreFundedWarrantsMember_24aa45cc-e25e-483f-a319-648ac5fe7d73" xlink:href="cris-20250630.xsd#cris_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e0a08e66-ae5a-498a-a259-005fba238f85" xlink:to="loc_cris_PreFundedWarrantsMember_24aa45cc-e25e-483f-a319-648ac5fe7d73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_5d68ce87-28c6-4a71-952b-9f6e0e3ca2c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_383b741e-d38e-45a0-b212-ad0eec82eaa5" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_5d68ce87-28c6-4a71-952b-9f6e0e3ca2c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_7b3d88cc-2e7f-46ed-8277-d18430493904" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_383b741e-d38e-45a0-b212-ad0eec82eaa5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_7b3d88cc-2e7f-46ed-8277-d18430493904" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/LossPerCommonShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#LossPerCommonShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/LossPerCommonShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_ce5cc0ad-ac7f-4f4c-9c0f-e4fdacab5c84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_bfc2e469-c6b4-4729-b4ba-4bcc9c1eccb9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_ce5cc0ad-ac7f-4f4c-9c0f-e4fdacab5c84" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_bfc2e469-c6b4-4729-b4ba-4bcc9c1eccb9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8623fbf7-8163-4610-a5e9-752bd89cdcc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_bfc2e469-c6b4-4729-b4ba-4bcc9c1eccb9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8623fbf7-8163-4610-a5e9-752bd89cdcc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8623fbf7-8163-4610-a5e9-752bd89cdcc7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8623fbf7-8163-4610-a5e9-752bd89cdcc7" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8623fbf7-8163-4610-a5e9-752bd89cdcc7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8623fbf7-8163-4610-a5e9-752bd89cdcc7" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_October2024CommonWarrantsMember_6380d0e8-5074-40e7-9390-ad2570353a03" xlink:href="cris-20250630.xsd#cris_October2024CommonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:to="loc_cris_October2024CommonWarrantsMember_6380d0e8-5074-40e7-9390-ad2570353a03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_March2025CommonWarrantsMember_526d937e-a544-4a11-b64b-c7ce3105cf30" xlink:href="cris-20250630.xsd#cris_March2025CommonWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:to="loc_cris_March2025CommonWarrantsMember_526d937e-a544-4a11-b64b-c7ce3105cf30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_79c5b741-ce85-4751-941d-1043ae0e9395" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:to="loc_us-gaap_EmployeeStockOptionMember_79c5b741-ce85-4751-941d-1043ae0e9395" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_abb7426f-5ba9-4bc2-92bd-6baef33241ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:to="loc_us-gaap_RestrictedStockMember_abb7426f-5ba9-4bc2-92bd-6baef33241ab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_6df7f145-14ba-4297-9566-f13cf850007a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2566fb23-82ba-47fd-bfd1-f46c08000e38" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_6df7f145-14ba-4297-9566-f13cf850007a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_5123d1b6-3bdd-4fba-a470-e10fd6ce6d90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_ce5cc0ad-ac7f-4f4c-9c0f-e4fdacab5c84" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_5123d1b6-3bdd-4fba-a470-e10fd6ce6d90" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.curis.com/role/SegmentInformationDetails" xlink:type="simple" xlink:href="cris-20250630.xsd#SegmentInformationDetails"/>
  <link:definitionLink xlink:role="http://www.curis.com/role/SegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_27f494b5-bb83-4019-b60a-5ba5128b09b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_27f494b5-bb83-4019-b60a-5ba5128b09b7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_a580e643-aba5-4488-8252-51056c9dca84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_27f494b5-bb83-4019-b60a-5ba5128b09b7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_a580e643-aba5-4488-8252-51056c9dca84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_a580e643-aba5-4488-8252-51056c9dca84_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_a580e643-aba5-4488-8252-51056c9dca84" xlink:to="loc_us-gaap_SegmentDomain_a580e643-aba5-4488-8252-51056c9dca84_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9e880da9-00ac-413d-be99-c2b3c983bf44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_a580e643-aba5-4488-8252-51056c9dca84" xlink:to="loc_us-gaap_SegmentDomain_9e880da9-00ac-413d-be99-c2b3c983bf44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ReportableSegmentMember_bbec44ca-948c-4963-828d-ec956a0260d2" xlink:href="cris-20250630.xsd#cris_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_9e880da9-00ac-413d-be99-c2b3c983bf44" xlink:to="loc_cris_ReportableSegmentMember_bbec44ca-948c-4963-828d-ec956a0260d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesNetOfInterestExpense_ebeb347c-00db-435f-b0f5-dd90270d2709" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesNetOfInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_us-gaap_RevenuesNetOfInterestExpense_ebeb347c-00db-435f-b0f5-dd90270d2709" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_9223a373-f85d-4e48-9ff6-c3fe15e4b26e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_9223a373-f85d-4e48-9ff6-c3fe15e4b26e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_ResearchAndDevelopmentEmployeeRelatedCosts_3fb862ec-b8db-4364-88bc-73bbe267acb9" xlink:href="cris-20250630.xsd#cris_ResearchAndDevelopmentEmployeeRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_cris_ResearchAndDevelopmentEmployeeRelatedCosts_3fb862ec-b8db-4364-88bc-73bbe267acb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_cris_GeneralAndAdministrativeEmployeeRelatedCosts_197c10d4-ded4-4145-b30b-77fbf3360c57" xlink:href="cris-20250630.xsd#cris_GeneralAndAdministrativeEmployeeRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_cris_GeneralAndAdministrativeEmployeeRelatedCosts_197c10d4-ded4-4145-b30b-77fbf3360c57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_0ae94dfa-cfca-410e-bc84-51a5e4844542" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_0ae94dfa-cfca-410e-bc84-51a5e4844542" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_d54dea51-555b-4ac3-a4f6-c9de677e0955" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_d54dea51-555b-4ac3-a4f6-c9de677e0955" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_37c4a8cf-5c76-40df-975a-362f9cfd57cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e0d83873-57d1-40e8-bbc2-0217ee4449a9" xlink:to="loc_us-gaap_NetIncomeLoss_37c4a8cf-5c76-40df-975a-362f9cfd57cb" xlink:type="arc" order="6"/>
  </link:definitionLink>
</link:linkbase>
