<SEC-DOCUMENT>0001104659-26-001317.txt : 20260106
<SEC-HEADER>0001104659-26-001317.hdr.sgml : 20260106
<ACCEPTANCE-DATETIME>20260106161757
ACCESSION NUMBER:		0001104659-26-001317
CONFORMED SUBMISSION TYPE:	S-8 POS
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20260106
DATE AS OF CHANGE:		20260106
EFFECTIVENESS DATE:		20260106

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Mersana Therapeutics, Inc.
		CENTRAL INDEX KEY:			0001442836
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		EIN:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		S-8 POS
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	333-276492
		FILM NUMBER:		26511763

	BUSINESS ADDRESS:	
		STREET 1:		840 MEMORIAL DRIVE
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139
		BUSINESS PHONE:		617-498-0020

	MAIL ADDRESS:	
		STREET 1:		840 MEMORIAL DRIVE
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MERSANA THERAPEUTICS INC
		DATE OF NAME CHANGE:	20080813
</SEC-HEADER>
<DOCUMENT>
<TYPE>S-8 POS
<SEQUENCE>1
<FILENAME>tm261736d22_s8pos.htm
<DESCRIPTION>S-8 POS
<TEXT>
<HTML>
<HEAD>
     <TITLE></TITLE>
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<BODY STYLE="font: 10pt Times New Roman, Times, Serif">

<P STYLE="text-align: center; margin-top: 0; margin-bottom: 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>As filed with the Securities and Exchange Commission
on January&nbsp;6, 2026</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-219388</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-222845</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-230159</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-236775</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-255975</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-263085</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-270110</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-276492</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: right"><B>Registration No.&nbsp;333-284273</B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"></P>

<!-- Field: Rule-Page --><DIV STYLE="width: 100%"><DIV STYLE="font-size: 1pt; border-top: Black 2pt solid; border-bottom: Black 1pt solid">&nbsp;</DIV></DIV><!-- Field: /Rule-Page -->

<P STYLE="font: 10pt Times New Roman, Times, Serif; text-align: center; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 18pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>UNITED STATES</B>&nbsp;</P>

<P STYLE="font: 18pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SECURITIES AND EXCHANGE COMMISSION</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Washington, D.C. 20549</B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="border-top: Black 1pt solid; font: 10pt Times New Roman, Times, Serif; text-align: center; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-219388</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-222845</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-230159</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-236775</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-255975</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-263085</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-270110</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-276492</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>POST-EFFECTIVE AMENDMENT NO. 1 TO FORM&nbsp;S-8
REGISTRATION STATEMENT NO. 333-284273</B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B><I>Under</I></B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B><I>The Securities Act of 1933</I></B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="border-top: Black 1pt solid; font: 10pt Times New Roman, Times, Serif; text-align: center; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 24pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>MERSANA THERAPEUTICS,&nbsp;INC.</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>(Exact name of registrant as specified in its
charter)</B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="border-top: Black 1pt solid; font: 10pt Times New Roman, Times, Serif; text-align: center; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
  <TR>
    <TD STYLE="width: 49%">&nbsp;</TD>
    <TD STYLE="vertical-align: bottom; width: 2%">&nbsp;</TD>
    <TD STYLE="width: 49%">&nbsp;</TD></TR>
  <TR>
    <TD STYLE="vertical-align: top; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Delaware</B></FONT></TD>
    <TD STYLE="vertical-align: bottom; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>04-3562403</B></FONT></TD></TR>
  <TR>
    <TD STYLE="vertical-align: top; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>(State or other jurisdiction of<BR>
incorporation or organization)</B></FONT></TD>
    <TD STYLE="vertical-align: bottom; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>(I.R.S. Employer<BR>
Identification No.)</B></FONT></TD></TR>
  <TR>
    <TD>&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD></TR>
  <TR>
    <TD STYLE="vertical-align: top">
    <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>840 Memorial Drive</B></P>
    <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Cambridge, Massachusetts</B></P></TD>
    <TD STYLE="vertical-align: bottom; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: bottom; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>02139</B></FONT></TD></TR>
  <TR>
    <TD STYLE="vertical-align: top; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>(Address of Principal Executive Offices)</B></FONT></TD>
    <TD STYLE="vertical-align: bottom; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>(Zip Code)</B></FONT></TD></TR>
  </TABLE>
<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Mersana Therapeutics,&nbsp;Inc.
2007 Stock Incentive Plan, as amended</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Mersana Therapeutics,&nbsp;Inc.
2017 Stock Incentive Plan</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Mersana Therapeutics,&nbsp;Inc.
2017 Employee Stock Purchase Plan</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Inducement Stock Option
Awards</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Mersana Therapeutics,&nbsp;Inc.
2022 Inducement Stock Incentive Plan&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>(Full title of the plans)</B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="border-top: Black 1pt solid; font: 10pt Times New Roman, Times, Serif; text-align: center; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; text-align: center; margin-top: 0pt; margin-bottom: 0pt"><B>Jeremy Bender, Ph.D.,
M.B.A.</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Chief Executive Officer and President</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Day One Biopharmaceuticals,
Inc.</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>1800 Sierra Point Parkway, Suite 200</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>Brisbane, California 94005</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>(650) 484-0899</B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>(Name, address,
and telephone number, including area code, of agent for service)</B></P>

<P STYLE="border-bottom: black 1pt solid; font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B><I>Copy to:</I></B></P>

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Robert A. Freedman</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>David Michaels</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Julia Forbess</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Fenwick&nbsp;&amp;
West LLP</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>401 Union Street,
Floor 5</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Seattle, Washington
98101</B>&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt; text-align: center"><B>(206)
389-4510</B></P>

<P STYLE="border-bottom: Black 1pt solid; text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Indicate by check mark whether the registrant is a large accelerated
filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions
of &#8220;large accelerated filer,&#8221; &#8220;accelerated filer,&#8221; &#8220;smaller reporting company,&#8221; and &#8220;emerging
growth company&#8221; in Rule&nbsp;12b-2 of the Exchange Act.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
  <TR>
    <TD>&nbsp;</TD>
    <TD STYLE="vertical-align: bottom">&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD STYLE="vertical-align: bottom">&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD STYLE="vertical-align: bottom">&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
  <TR STYLE="vertical-align: bottom">
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Large accelerated filer</FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><FONT STYLE="font-family: Wingdings">&#168;</FONT></FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Accelerated filer</FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><FONT STYLE="font-family: Wingdings">&#168;</FONT></FONT></TD></TR>
  <TR>
    <TD>&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD></TR>
  <TR STYLE="vertical-align: bottom">
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Non-accelerated filer</FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><FONT STYLE="font-family: Wingdings">&#120;</FONT></FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Smaller reporting company</FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><FONT STYLE="font-family: Wingdings">&#120;</FONT></FONT></TD></TR>
  <TR>
    <TD>&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD>
    <TD COLSPAN="2">&nbsp;</TD></TR>
  <TR STYLE="vertical-align: bottom">
    <TD>&nbsp;</TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Emerging growth company</FONT></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><FONT STYLE="font-family: Wingdings">&#168;</FONT></FONT></TD></TR>
  </TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-family: Times New Roman, Times, Serif">If an emerging
growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any
new or revised financial accounting standards provided pursuant to Section&nbsp;7(a)(2)(B)&nbsp;of the Securities Act. </FONT><FONT STYLE="font-family: Wingdings">&#168;</FONT><FONT STYLE="font-family: Wingdings; color: #0070c0"></FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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    <DIV STYLE="break-before: page; margin-top: 6pt; margin-bottom: 12pt"><P STYLE="margin: 0pt">&nbsp;</P></DIV>
    <!-- Field: /Page -->

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>DEREGISTRATION OF SECURITIES</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">These Post-Effective Amendments (these &#8220;<U>Post-Effective Amendments</U>&#8221;)
filed by Mersana Therapeutics,&nbsp;Inc. (the &#8220;<U>Registrant</U>&#8221;) relate to the following registration statements on Form&nbsp;S-8
(together, the &#8220;<U>Registration Statements</U>&#8221;):</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">1.</TD><TD>Registration Statement No.&nbsp;333-219388, registering (i)&nbsp;125,665 shares of common stock, $0.0001 par value per share, of the
Registrant (&#8220;<U>Common Stock</U>&#8221;) issuable under the Registrant&#8217;s 2007 Stock Incentive Plan, as amended (the &#8220;<U>2007
Plan</U>&#8221;), (ii)&nbsp;90,200 shares of Common Stock issuable under the Registrant&#8217;s 2017 Stock Incentive Plan (the &#8220;<U>2017
Plan</U>&#8221;) and (iii)&nbsp;9,000 shares of Common Stock issuable under the Registrant&#8217;s 2017 Employee Stock Purchase Plan (the
 &#8220;<U>2017 ESPP</U>&#8221;), which was filed with the U.S. Securities and Exchange Commission (the &#8220;<U>SEC</U>&#8221;) on July&nbsp;21,
2017.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">2.</TD><TD>Registration Statement No.&nbsp;333-222845, registering 36,424 shares of Common Stock issuable under the 2017 Plan, which was filed
with the SEC on February&nbsp;2, 2018.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">3.</TD><TD>Registration Statement No.&nbsp;333-230159, registering (i)&nbsp;37,175 shares of Common Stock issuable under the 2017 Plan and (ii)&nbsp;9,293
shares of Common Stock issuable under the 2017 ESPP, which was filed with the SEC on March&nbsp;8, 2019.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">4.</TD><TD>Registration Statement No.&nbsp;333-236775, registering (i)&nbsp;72,620 shares of Common Stock issuable under the 2017 Plan and (ii)&nbsp;18,000
shares of Common Stock issuable under the 2017 ESPP, which was filed with the SEC on February&nbsp;28, 2020.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">5.</TD><TD>Registration Statement No.&nbsp;333-255975, registering (i)&nbsp;110,146 shares of Common Stock issuable under the 2017 Plan and (ii)&nbsp;an
aggregate of 21,300 shares of Common Stock issuable under Inducement Stock Options granted to certain employees of the Registrant on August&nbsp;31,
2020, November&nbsp;30, 2020, January&nbsp;19, 2021 and April&nbsp;26, 2021, which was filed with the SEC on May&nbsp;10, 2021.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">6.</TD><TD>Registration Statement No.&nbsp;333-263085, registering (i)&nbsp;117,934 shares of Common Stock issuable under the 2017 Plan, (ii)&nbsp;80,000
shares of Common Stock issuable under the Registrant&#8217;s 2022 Inducement Stock Incentive Plan and (iii)&nbsp;an aggregate of 9,000
shares of Common Stock issuable under Inducement Stock Options granted to certain employees of the Registrant on August&nbsp;16, 2021
and October&nbsp;25, 2021, which was filed with the SEC on February&nbsp;28, 2022.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">7.</TD><TD>Registration Statement No.&nbsp;333-270110, registering (i)&nbsp;168,231 shares of Common Stock issuable under the 2017 Plan and (ii)&nbsp;18,000
shares of Common Stock issuable under the 2017 ESPP, which was filed with the SEC on February&nbsp;28, 2023.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">8.</TD><TD>Registration Statement No.&nbsp;333-276492, registering (i)&nbsp;193,138 shares of Common Stock issuable under the 2017 Plan and (ii)&nbsp;18,000
shares of Common Stock issuable under the 2017 ESPP, which was filed with the SEC on January&nbsp;12, 2024.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLPADDING="0" CELLSPACING="0" WIDTH="100%" STYLE="font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"><TR STYLE="vertical-align: top">
<TD STYLE="width: 0.25in"></TD><TD STYLE="width: 0.25in">9.</TD><TD>Registration Statement No.&nbsp;333-284273, registering (i)&nbsp;185,039 shares of Common Stock issuable under the 2017 Plan and (ii)&nbsp;18,000
shares of Common Stock issuable under the 2017 ESPP, which was filed with the SEC on January&nbsp;14, 2025.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">All share numbers set forth above reflect a 1-for-25 reverse stock
split of Common Stock, that became effective on July&nbsp;25, 2025.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">On January&nbsp;6, 2026, pursuant to the Agreement and Plan of
Merger, dated as of November&nbsp;12, 2025 (the &#8220;<U>Merger Agreement</U>&#8221;), by and among the Registrant, Day One
Biopharmaceuticals,&nbsp;Inc., a Delaware corporation (&#8220;<U>Parent</U>&#8221;) and Emerald Merger Sub,&nbsp;Inc., a Delaware
corporation and a direct wholly-owned subsidiary of Parent (&#8220;<U>Purchaser</U>&#8221;), Purchaser merged with and into the
Registrant, with the Registrant surviving as a direct wholly-owned subsidiary of Parent.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">As a result of the transactions contemplated by the Merger
Agreement, the Registrant has terminated any and all offerings and sales of securities pursuant to the Registration Statements. In
accordance with the undertakings made by the Registrant in the Registration Statements to remove from registration, by means of a
post-effective amendment, any of the securities of the Registrant registered under the Registration Statements which remain unsold
at the termination of the offerings, the Registrant hereby terminates the effectiveness of the Registration Statements and removes
from registration all of the securities that remain unsold under the Registration Statements as of the date hereof, if any. The
Registrant is filing these Post-Effective Amendments to withdraw and remove from registration all securities registered pursuant to
the Registration Statements that remain unsold as of the date hereof. The Registration Statements are hereby amended, as
appropriate, to reflect the deregistration of such securities. After giving effect to these Post-Effective Amendments, there will be
no remaining securities registered by the Registrant pursuant to the Registration Statements.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SIGNATURE</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form&nbsp;S-8 and
has duly caused these Post-Effective Amendments to be signed on its behalf by the undersigned, thereunto duly authorized, in the City
of Brisbane, State of California, on January&nbsp;6, 2026.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
  <TR STYLE="vertical-align: top">
    <TD>&nbsp;</TD>
    <TD COLSPAN="2" STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>MERSANA THERAPEUTICS,&nbsp;INC.</B></FONT></TD></TR>
  <TR>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD>
    <TD>&nbsp;</TD></TR>
  <TR>
    <TD STYLE="width: 50%">&nbsp;</TD>
    <TD STYLE="vertical-align: top; font-size: 10pt; width: 6%"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">By:</FONT></TD>
    <TD STYLE="vertical-align: bottom; border-bottom: black 1pt solid; width: 44%">/s/ Charles N. York II</TD>
    </TR>
  <TR STYLE="vertical-align: bottom">
    <TD>&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Name:</FONT></TD>
    <TD STYLE="font-size: 10pt">Charles N. York II, M.B.A.</TD>
    </TR>
  <TR STYLE="vertical-align: bottom">
    <TD>&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Title:</FONT></TD>
    <TD STYLE="font-size: 10pt">Chief Executive Officer</TD>
    </TR>
  </TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Pursuant to Rule&nbsp;478 under the Securities Act of 1933, as amended,
no other person is required to sign these Post-Effective Amendments.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

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