<SEC-DOCUMENT>0001104659-20-040376.txt : 20200330
<SEC-HEADER>0001104659-20-040376.hdr.sgml : 20200330
<ACCEPTANCE-DATETIME>20200330161529
ACCESSION NUMBER:		0001104659-20-040376
CONFORMED SUBMISSION TYPE:	8-K
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20200330
ITEM INFORMATION:		Other Events
ITEM INFORMATION:		Financial Statements and Exhibits
FILED AS OF DATE:		20200330
DATE AS OF CHANGE:		20200330

FILER:

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

	FILING VALUES:
		FORM TYPE:		8-K
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-38129
		FILM NUMBER:		20757213

	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>8-K
<SEQUENCE>1
<FILENAME>tm2014197-1_8k.htm
<DESCRIPTION>FORM 8-K
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<P STYLE="margin: 0">&nbsp;</P>

<P STYLE="margin: 0"></P>

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

<P STYLE="font: 18pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SECURITIES AND EXCHANGE COMMISSION</B></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="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 18pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>FORM 8-K</B></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: center"><B>CURRENT REPORT</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934</B></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: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Date
of Report (Date of earliest event reported): </FONT><B>March 30, 2020</B></P>

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

<P STYLE="font: 18pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>MERSANA THERAPEUTICS, INC.</B></P>

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

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

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<TD STYLE="text-align: center; vertical-align: top; width: 32%"><B>Delaware</B> </TD>
<TD STYLE="text-align: center; vertical-align: bottom; width: 2%"><B>&nbsp;</B> &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top; width: 32%"><B>001-38129</B> </TD>
<TD STYLE="text-align: center; vertical-align: bottom; width: 2%"><B>&nbsp;</B> &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top; width: 32%"><B>04-3562403</B> </TD></TR>
<TR>
<TD STYLE="text-align: center; vertical-align: top">(State or other jurisdiction of<BR> incorporation) &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: bottom">&nbsp; &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top">(Commission File Number) &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: bottom">&nbsp; &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top">(IRS Employer<BR> Identification No.) &nbsp;</TD></TR>
</TABLE>

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

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif; border-collapse: collapse">
<TR>
<TD STYLE="text-align: center; vertical-align: top; width: 49%"><B>840 Memorial Drive</B> <B>Cambridge, MA 02139</B></TD>
<TD STYLE="text-align: center; vertical-align: bottom; width: 2%">&nbsp; &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top; width: 49%">&nbsp; &nbsp;</TD></TR>
<TR>
<TD STYLE="text-align: center; vertical-align: top"><B>Cambridge, MA</B> </TD>
<TD STYLE="text-align: center; vertical-align: bottom"><B>&nbsp;</B> &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top"><B>02139</B> </TD></TR>
<TR>
<TD STYLE="text-align: center; vertical-align: top">(Address of principal executive offices) &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: bottom">&nbsp; &nbsp;</TD>
<TD STYLE="text-align: center; vertical-align: top">(Zip Code) &nbsp;</TD></TR>
</TABLE>

<P STYLE="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"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">(Registrant&rsquo;s
telephone number, including area code): </FONT><B>(617) 498-0020</B></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: center"><B>Not Applicable</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Former name or former address, if changed
since last report)</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">Check the appropriate box below if the Form 8-K filing is intended
to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:</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 0pt 0.25in; text-indent: -0.25in"><FONT STYLE="font-family: Wingdings">&#168;</FONT><FONT STYLE="font-size: 10pt">&nbsp;</FONT>Written
communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.25in; text-indent: -0.25in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.25in; text-indent: -0.25in"><FONT STYLE="font-family: Wingdings">&#168;</FONT><FONT STYLE="font-size: 10pt">&nbsp;</FONT>Soliciting
material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.25in; text-indent: -0.25in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.25in; text-indent: -0.25in"><FONT STYLE="font-family: Wingdings">&#168;</FONT><FONT STYLE="font-size: 10pt">&nbsp;</FONT>Pre-commencement
communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.25in; text-indent: -0.25in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.25in; text-indent: -0.25in"><FONT STYLE="font-family: Wingdings">&#168;</FONT><FONT STYLE="font-size: 10pt">&nbsp;</FONT>Pre-commencement
communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))</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; color: #221e1f">Securities registered pursuant to Section 12(b)
of the Act:</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; color: #221e1f">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD STYLE="border: Black 1pt solid; padding: 2pt 3pt; width: 33%; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt; color: black">Title of each class</FONT></TD>
    <TD STYLE="border-top: Black 1pt solid; padding: 2pt 3pt; width: 28%; border-right: Black 1pt solid; border-bottom: Black 1pt solid; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt; color: black">Trading Symbol(s)</FONT></TD>
    <TD STYLE="border-top: Black 1pt solid; padding: 2pt 3pt; width: 39%; border-right: Black 1pt solid; border-bottom: Black 1pt solid; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt; color: black">Name of each exchange on which<BR>
 registered</FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="border-right: Black 1pt solid; padding: 2pt 3pt; border-bottom: Black 1pt solid; border-left: Black 1pt solid; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt; color: black">Common Stock, $0.0001 par value</FONT></TD>
    <TD STYLE="border-right: Black 1pt solid; padding: 2pt 3pt; border-bottom: Black 1pt solid; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt; color: black">MRSN</FONT></TD>
    <TD STYLE="border-right: Black 1pt solid; padding: 2pt 3pt; border-bottom: Black 1pt solid; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt; color: black">The Nasdaq Global Select Market</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">Indicate by check mark whether the registrant is an emerging
growth company as defined in Rule 405 of the Securities Act of 1933 (&sect;230.405 of this chapter) or Rule 12b-2 of the Securities
Exchange Act of 1934 (&sect;240.12b-2 of this chapter).</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">Emerging growth company <FONT STYLE="font-family: Wingdings">&#120;</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">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 13(a) of the Exchange Act. <FONT STYLE="font-family: Wingdings">&#120;</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>

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

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<TD STYLE="width: 1in"><B>Item 8.01</B></TD><TD><B>Other Events.</B></TD></TR></TABLE>

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

<P STYLE="text-align: justify; font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">On March 30, 2020, Mersana Therapeutics, Inc. (the &ldquo;Company&rdquo;),
issued a press release providing updated Phase 1 dose escalation data for XMT-1536. The Company&rsquo;s press release is attached
as Exhibit 99.1 to this current report and is incorporated herein by reference.</P>

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

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<TR STYLE="vertical-align: top">
    <TD STYLE="width: 1in"><B>Item 9.01 </B></TD>
    <TD><B>Financial Statements and Exhibits.</B></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">(d) Exhibits</P>

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

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif; border-collapse: collapse">
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    <TD STYLE="border-bottom: Black 1pt solid; width: 10%; font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Exhibit No.</B></FONT></TD>
    <TD STYLE="width: 2%; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="border-bottom: Black 1pt solid; width: 88%; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Description</B></FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">99.1</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">Press Release by Mersana Therapeutics, Inc., on March 30, 2020</FONT></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</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>EXHIBIT INDEX</B></P>

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

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif; border-collapse: collapse">
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    <TD STYLE="border-bottom: Black 1pt solid; width: 10%; font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>No.</B></FONT></TD>
    <TD STYLE="width: 2%; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="border-bottom: Black 1pt solid; width: 88%; font-size: 10pt; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Description</B></FONT></TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD STYLE="font-size: 10pt"><A HREF="tm2014197d1_ex99-1.htm" STYLE="-sec-extract: exhibit"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">99.1</FONT></A></TD>
    <TD STYLE="font-size: 10pt">&nbsp;</TD>
    <TD STYLE="font-size: 10pt"><A HREF="tm2014197d1_ex99-1.htm" STYLE="-sec-extract: exhibit"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">Press Release by Mersana Therapeutics, Inc., on March 30, 2020</FONT></A></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

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

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

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

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

<P STYLE="text-align: justify; font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Pursuant to the requirements of the Securities Exchange Act
of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.</P>

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

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<TR STYLE="vertical-align: top">
<TD STYLE="width: 51%">&nbsp; &nbsp;</TD>
<TD STYLE="width: 5%">&nbsp; &nbsp;</TD>
<TD STYLE="width: 44%"><B>MERSANA THERAPEUTICS, INC.</B> &nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
<TD>&nbsp; &nbsp;</TD>
<TD>&nbsp; &nbsp;</TD>
<TD>&nbsp; &nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
<TD>&nbsp;</TD>
<TD>&nbsp;</TD>
<TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
<TD>&nbsp; &nbsp;</TD>
<TD STYLE="font-size: 10pt"><FONT STYLE="font: 10pt Times New Roman, Times, Serif">By:&nbsp;</FONT></TD>
<TD STYLE="border-bottom: black 1pt solid; font-size: 10pt"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">/s/
Brian DeSchuytner</FONT></TD></TR>
<TR STYLE="vertical-align: top">
<TD>&nbsp; &nbsp;</TD>
<TD>&nbsp; &nbsp;</TD>
<TD>Brian DeSchuytner<BR> Senior Vice President, Finance &amp; Product Strategy &nbsp;</TD></TR>
</TABLE>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Date: March 30, 2020</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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<DOCUMENT>
<TYPE>EX-99.1
<SEQUENCE>2
<FILENAME>tm2014197d1_ex99-1.htm
<DESCRIPTION>EXHIBIT 99.1
<TEXT>
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<P STYLE="font: 10pt Times New Roman, Times, Serif; text-align: right; margin: 0pt 0"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Exhibit
99.1</B></FONT></P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Mersana Therapeutics Reports Updated
Data from the XMT-1536 Phase 1 Dose Escalation Study </B></P>

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

<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"> - <I>&nbsp;&nbsp;Well tolerated at doses up to 43 mg/m<SUP>2 </SUP>with encouraging activity in heavily pre-treated patient populations</I></P>



<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"> - &nbsp;&nbsp;<I>Favorable trend towards higher response rates with higher NaPi2b expression</I></P>



<P STYLE="text-align: center; font: 10pt Times New Roman, Times, Serif; margin-top: 0pt; margin-bottom: 0pt"> - &nbsp;&nbsp;<I>On track for interim disclosure of Phase 1 expansion cohort data in Q2 2020</I></P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.5in; text-align: justify">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>CAMBRIDGE, Mass., March 30, 2020</B>
-- Mersana Therapeutics, Inc. (NASDAQ:MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a
pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, today announced updated efficacy
and safety data in patients with ovarian cancer and non-small cell lung cancer (NSCLC) adenocarcinoma from its ongoing Phase 1
dose escalation study evaluating XMT-1536. The Company will host a call today, Monday, March 30, 2020, at 5:00 pm ET during which
investigator Debra L. Richardson, MD, Associate Professor of Gynecologic Oncology at the Stephenson Cancer Center at the University
of Oklahoma Health Sciences Center and the Sarah Cannon Research Institute and members of the Mersana executive team will present
and discuss these data.</P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><FONT STYLE="background-color: white">&ldquo;These
data demonstrate that XMT-1536, our first-in-class Dolaflexin ADC targeting NaPi2b, delivers confirmed responses and durable stable
disease in heavily pretreated ovarian cancer and NSCLC adenocarcinoma patients who have exhausted all other treatment options.
These data also show that XMT-1536 is well tolerated without the severe toxicities of other ADC platforms such as neutropenia,
neuropathy and ocular toxicity. Moreover, these data establish the potential for a biomarker-response relationship to identify
patients most likely to benefit from XMT-1536,&rdquo; said Anna Protopapas, President and Chief Executive Officer of Mersana Therapeutics.
 &ldquo;We look forward to advancing XMT-1536 for both ovarian cancer and NSCLC adenocarcinoma patients. Having already accumulated
meaningful patient experience in the expansion cohorts, we remain on track to provide an interim update in the second quarter of
2020.&rdquo;</FONT></P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Of the 59 patients enrolled, tumor types
included 37 ovarian cancer, 11 NSCLC adenocarcinoma, and 11 other tumor types previously disclosed at lower dose levels. Patients
were heavily pre-treated, with a median of five prior lines of treatment (range 1-10). These data include new patients dosed at
30, 36 and 43 mg/m<SUP>2</SUP>. The majority of the ovarian cancer patients had received prior bevacizumab or PARP inhibitors.
All NSCLC adenocarcinoma patients had received prior platinum and immunotherapy. Updated and new data as of February 3, 2020 includes:</P>

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

<TABLE CELLPADDING="0" CELLSPACING="0" STYLE="width: 100%; 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"><FONT STYLE="font-family: Symbol">&middot;</FONT></TD><TD STYLE="text-align: justify"><FONT STYLE="font-family: Times New Roman, Times, Serif"><B>Safety profile consistent with previously
reported data at lower doses. </B></FONT></TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify">The most common treatment-related adverse events (TRAEs) were Grade 1-2 nausea, fatigue, headache
and the most frequent Grade 3 TRAE was transient AST elevation.</TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify">There were no dose limiting toxicities observed in the 43 mg/m<SUP>2 </SUP>cohort.</TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify">There was no reported severe neutropenia, peripheral neuropathy or ocular toxicity.</TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 0.5in; text-align: justify"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-align: justify"></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-align: justify">&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"><FONT STYLE="font-family: Symbol">&middot;</FONT></TD><TD STYLE="text-align: justify"><FONT STYLE="font-family: Times New Roman, Times, Serif"><B>Additional confirmed responses in heavily
pretreated patients and favorable biomarker-response trend observed.</B></FONT></TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify">First confirmed partial response seen in a NSCLC adenocarcinoma patient with prior treatments including
carboplatin, pemetrexed, paclitaxel and nivolumab.</TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify">At the 43 mg/m<SUP>2</SUP> dose level, 2/7 (29%) patients achieved partial responses (PRs) and
4/7 (57%) patients achieved stable disease (SD) for a disease control rate (DCR) of 6/7 (86%). In January 2020, the expansion portion
of the Phase 1 study dose was amended from 36 mg/m<SUP>2</SUP> to 43 mg/m<SUP>2</SUP> for newly enrolled patients.</TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify">For the subset of evaluable patients treated at <B><U>&gt;</U></B>30 mg/m<SUP>2</SUP> who had higher
NaPi2b expression, 5/15 (33%) achieved PR and 6/15 (40%) achieved SD for a DCR of 11/15 (73%).</TD></TR></TABLE>

<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: 0.75in"></TD><TD STYLE="width: 0.25in">o</TD><TD STYLE="text-align: justify"><FONT STYLE="font-size: 10pt; color: windowtext">In contrast, for the subset of evaluable patients
treated at <B><U>&gt;</U></B>30 mg/m<SUP>2</SUP> who had lower NaPi2b expression, 0/9 (0%) achieved PR and 5/9 (55%) achieved SD
for a DCR of 5/9 (55%). </FONT></TD></TR></TABLE>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">&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 COLSPAN="2" STYLE="border-bottom: Black 1pt solid"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Response - Ovarian Cancer <BR>
and NSCLC <BR>
adenocarcinoma N=39*</B></FONT></TD>
    <TD STYLE="padding-bottom: 1pt">&nbsp;</TD>
    <TD COLSPAN="7" STYLE="vertical-align: bottom; text-align: center; border-bottom: Black 1pt solid"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>N (%)</B></FONT></TD>
    <TD STYLE="padding-bottom: 1pt">&nbsp;</TD></TR>
<TR STYLE="vertical-align: top">
    <TD COLSPAN="2" STYLE="padding-bottom: 1pt">&nbsp;</TD>
    <TD STYLE="padding-bottom: 1pt; text-align: center">&nbsp;</TD>
    <TD STYLE="vertical-align: bottom; border-bottom: Black 1pt solid; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>All</B></FONT></TD>
    <TD STYLE="padding-bottom: 1pt">&nbsp;</TD>
    <TD STYLE="border-bottom: Black 1pt solid; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Higher<BR>
 NaPi2b <SUP>o</SUP></B></FONT></TD>
    <TD STYLE="padding-bottom: 1pt">&nbsp;</TD>
    <TD STYLE="border-bottom: Black 1pt solid; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Lower<BR>
 NaPi2b <SUP>oo</SUP></B></FONT></TD>
    <TD STYLE="padding-bottom: 1pt">&nbsp;</TD>
    <TD STYLE="border-bottom: Black 1pt solid; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>Indeterminate<BR>
 NaPi2b **</B></FONT></TD>
    <TD STYLE="padding-bottom: 1pt">&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD ROWSPAN="4" STYLE="width: 15%"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>20 mg/m<SUP>2</SUP></B></FONT></TD>
    <TD STYLE="width: 28%"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">N</FONT></TD>
    <TD STYLE="width: 1%; text-align: center">&nbsp;</TD>
    <TD STYLE="width: 13%; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">10</FONT></TD>
    <TD STYLE="width: 1%">&nbsp;</TD>
    <TD STYLE="width: 13%; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">7</FONT></TD>
    <TD STYLE="width: 1%">&nbsp;</TD>
    <TD STYLE="width: 13%; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">2</FONT></TD>
    <TD STYLE="width: 1%">&nbsp;</TD>
    <TD STYLE="width: 13%; text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">1</FONT></TD>
    <TD STYLE="width: 1%">&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>PR</B></FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>1 (10%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>0 (0%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>0 (0%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>1 (100%)</B></FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">SD</FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">6 (60%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">4 (57%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">2 (100%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">0 (0%)</FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>DCR (PR+SD)</B></FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>7 (70%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>4 (57%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>2 (100%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>1 (100%)</B></FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: White">
    <TD ROWSPAN="4"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>30, 36, 40 mg/m<SUP>2</SUP></B></FONT></TD>
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">N</FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">22</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">12</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">7</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">3</FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: White">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>PR</B></FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>3 (14%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>3 (25%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>0 (0%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>0 (0%)</B></FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: White">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">SD</FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">10 (45%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">6 (50%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">3 (43%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">1 (33%)</FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: White">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>DCR (PR+SD)</B></FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>13 (59%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>9 (75%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>3 (43%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>1 (33%)</B></FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD ROWSPAN="4"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>43 mg/m<SUP>2</SUP></B></FONT></TD>
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">N</FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">7</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">3</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">2</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">2</FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>PR</B></FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>2 (29%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>2 (67%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>0 (0%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>0 (0%)</B></FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">SD</FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">4 (57%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">0 (0%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">2 (100%)</FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt">2 (100%)</FONT></TD>
    <TD>&nbsp;</TD></TR>
<TR STYLE="vertical-align: top; background-color: rgb(204,238,255)">
    <TD><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>DCR (PR+SD)</B></FONT></TD>
    <TD STYLE="text-align: center">&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>6 (86%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>2 (67%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>2 (100%)</B></FONT></TD>
    <TD>&nbsp;</TD>
    <TD STYLE="text-align: center"><FONT STYLE="font-family: Times New Roman, Times, Serif; font-size: 10pt"><B>2 (100%)</B></FONT></TD>
    <TD>&nbsp;</TD></TR>
</TABLE>


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

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">*Excludes 3 patients discontinued due to
investigator/patient choice and 1 without RECIST scan</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">**Hypocellular specimen/indeterminate for
H-score or not determined yet</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><SUP>O </SUP>Higher NaPi2b Expression:
at / above lowest H-score at which response observed (<U>&gt;</U>110)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><SUP>OO </SUP>Lower NaPi2b Expression:
below the lowest H-score at which response observed (&lt;110)</P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Mersana plans to enroll approximately 45
patients in each of the ovarian cancer and NSCLC adenocarcinoma patient cohorts in the expansion portion of the XMT-1536 Phase
1 study. The Company expects to present interim data from the dose expansion study in the second quarter of 2020.</P>

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

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

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>Conference Call Details</B></P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><FONT STYLE="color: windowtext">Mersana
Therapeutics will host a conference call and webcast today at 5:00 p.m. ET to review these data. To access the call, please dial
877-303-9226 (domestic) or 409-981-0870 (international) and provide the Conference ID 2889994. A live webcast of the presentation
will be available on the Investors &amp; Media section of the Mersana website at </FONT><U>www.mersana.com</U><FONT STYLE="color: windowtext">.
</FONT></P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify"><B>About Mersana Therapeutics</B></P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">Mersana Therapeutics is a clinical-stage
biopharmaceutical company using its differentiated and proprietary ADC platforms to rapidly develop novel ADCs with optimal efficacy,
safety and tolerability to meaningfully improve the lives of people fighting cancer. Mersana&rsquo;s lead product candidate, XMT-1536,
is in a Phase 1 proof-of-concept clinical trial in patients with tumors likely to express NaPi2b, including ovarian cancer and
NSCLC adenocarcinoma. Mersana&rsquo;s second product candidate targeting NaPi2b-expressing tumors, XMT-1592, is an ADC created
using Mersana&rsquo;s customizable and homogenous Dolasynthen platform. The Company&rsquo;s early stage programs include a B7-H4
targeting ADC, as well as a STING agonist ADC developed using the Company&rsquo;s Immunosynthen platform. In addition, multiple
partners are using Mersana&rsquo;s Dolaflexin platform to advance their ADC pipelines.</P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Forward-Looking Statements</B></P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: justify">This press release contains &ldquo;forward-looking&rdquo;
statements within the meaning of federal securities laws. These forward-looking statements are not statements of historical facts
and are based on management&rsquo;s beliefs and assumptions and on information currently available to management. Forward-looking
statements include information concerning the Company&rsquo;s business strategy and the design, progression and timing of its clinical
trials. Forward-looking statements generally can be identified by terms such as &ldquo;anticipates,&rdquo; &ldquo;believes,&rdquo;
 &ldquo;could,&rdquo; &ldquo;seeks,&rdquo; &ldquo;estimates,&rdquo; &ldquo;intends,&rdquo; &ldquo;may,&rdquo; &ldquo;plans,&rdquo;
 &ldquo;potential,&rdquo; &ldquo;predicts,&rdquo; &ldquo;projects,&rdquo; &ldquo;should,&rdquo; &ldquo;will,&rdquo; &ldquo;would&rdquo;
or similar expressions and the negatives of those terms. Forward-looking statements represent management&rsquo;s beliefs and assumptions
only as of the date of this press release. The Company&rsquo;s operations involve risks and uncertainties, many of which are outside
its control, and any one of which, or combination of which, could materially affect its results of operations and whether the forward-looking
statements ultimately prove to be correct. Factors that may materially affect the Company&rsquo;s results of operations and whether
these forward-looking statements prove to be correct include, among other things, that preclinical testing may not be predictive
of the results or success of ongoing or later preclinical or clinical trials, that the development and testing of the Company&rsquo;s
product candidates and new platforms will take longer and/or cost more than planned, including as a result of any impact of the
current pandemic, and that the identification of new product candidates will take longer than planned, as well as those listed
in the Company&rsquo;s Annual Report on Form 10-K filed on February 28, 2020, with the Securities and Exchange Commission (&ldquo;SEC&rdquo;)
and subsequent SEC filings. Except as required by law, the Company assumes no obligation to update these forward-looking statements
publicly, or to update the reasons actual results could differ materially from those anticipated in the forward-looking statements,
even if new information becomes available in the future.</P>

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

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Contact:</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">Investor &amp; Media Contact<BR>
Sarah Carmody</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">617-844-8577</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><U>scarmody@mersana.com</U></P>



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