<SEC-DOCUMENT>0001628280-25-049176.txt : 20251104
<SEC-HEADER>0001628280-25-049176.hdr.sgml : 20251104
<ACCEPTANCE-DATETIME>20251104203801
ACCESSION NUMBER:		0001628280-25-049176
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250827
FILED AS OF DATE:		20251104
DATE AS OF CHANGE:		20251104

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Oelschlager Kristen M
		CENTRAL INDEX KEY:			0001856565
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-38984
		FILM NUMBER:		251451394

	MAIL ADDRESS:	
		STREET 1:		C/O CASTLE BIOSCIENCES
		STREET 2:		505 S. FRIENDSWOOD DRIVE, SUITE 401
		CITY:			FRIENDSWOOD
		STATE:			TX
		ZIP:			77546

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CASTLE BIOSCIENCES INC
		CENTRAL INDEX KEY:			0001447362
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-MEDICAL LABORATORIES [8071]
		ORGANIZATION NAME:           	08 Industrial Applications and Services
		EIN:				770701774
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		505 S FRIENDSWOOD DRIVE
		STREET 2:		SUITE 401
		CITY:			FRIENDSWOOD
		STATE:			TX
		ZIP:			77546
		BUSINESS PHONE:		866-788-9007

	MAIL ADDRESS:	
		STREET 1:		505 S FRIENDSWOOD DRIVE
		STREET 2:		SUITE 401
		CITY:			FRIENDSWOOD
		STATE:			TX
		ZIP:			77546
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>wk-form4a_1762306678.xml
<DESCRIPTION>FORM 4/A
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2025-08-27</periodOfReport>

    <dateOfOriginalSubmission>2025-08-29</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001447362</issuerCik>
        <issuerName>CASTLE BIOSCIENCES INC</issuerName>
        <issuerTradingSymbol>CSTL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001856565</rptOwnerCik>
            <rptOwnerName>Oelschlager Kristen M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CASTLE BIOSCIENCES, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>505 S FRIENDSWOOD DRIVE, SUITE 401</rptOwnerStreet2>
            <rptOwnerCity>FRIENDSWOOD</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77546</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Operating Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-08-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>18007</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>21.69</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>100937</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>The Fritz Shorter Trust</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>52924</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This transaction was executed in multiple trades at prices ranging from $21.24 to $21.94, inclusive. The price reported above reflects the weighted-average sale price. The Reporting Person hereby undertakes to provide upon request to the Securities and Exchange Commission staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.</footnote>
        <footnote id="F2">On August 29, 2025, the Reporting Person filed a Form 4 which inadvertently reported that shares were sold by the Reporting Person directly.  In fact, as reported in this amendment, the shares were sold by the Fritz Shorter Trust (the &quot;Trust&quot;).  The original Form 4 also mistakenly indicated the wrong number of shares held by the Reporting Person directly and indirectly through the Trust. In fact, following this sale, the Reporting Person held 52,924 shares of common stock directly and 100,937 shares of common stock indirectly through the Trust. In addition, following a reconciliation of the reporting person's holdings, it was determined that the balance previously reported was understated by 68 shares, and the holdings reported herein have been adjusted accordingly.</footnote>
        <footnote id="F3">On March 19, 2025 and on August 22, 2025, the Reporting Person transferred 96,322 and 22,622 shares to the Trust. The transfer was not a change in beneficial ownership because the Reporting Person and her spouse are the trustees and sole beneficiaries of the Trust, the Trust is revocable and the Reporting Person has voting and investment power over the shares held by the Trust.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Frank Stokes, Attorney-in-fact</signatureName>
        <signatureDate>2025-11-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
