UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)
of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): ~~July~~August 2413, 2025

MERSANA THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

Delaware

001-38129

04-3562403

(State or other jurisdiction
of incorporation)

(Commission

File Number)

(IRS Employer

Identification No.)

840 Memorial Drive Cambridge, Massachusetts		02139
(Address of Principal Executive Offices)		(Zip Code)

Registrant’s telephone number, including area code: (617) 498-0020

Not Applicable

(Former name or former address, if changed since last report)

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 (see General Instruction A.2. below):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class	Trading Symbol(s)	Name of each exchange on which registered
Common Stock, $0.0001 par value	MRSN	The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ¨

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. ¨

Item 32.0302 ~~Material~~Results ~~Modification~~of toOperations ~~Rights~~and ofFinancial ~~Security Holders~~Condition.

ToOn ~~the~~August ~~extent~~13, ~~required~~2025, byMersana Therapeutics, ~~Item 3~~Inc.03 ~~of Form 8-K,~~ (the ~~information~~“Company”) ~~contained~~issued ina ~~Item~~press ~~5.03~~release ofannouncing ~~this~~business ~~Current~~updates ~~Report~~and onfinancial ~~Form 8-K~~results isfor ~~incorporated~~the ~~herein~~fiscal quarter byended ~~reference~~June 30, 2025.

The information furnished in this Item 52.0302, ~~Amendments~~including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to ~~Articles~~the liabilities of ~~Incorporation~~that section, nor shall such information be deemed incorporated by reference in any filing by the Company with the Securities and Exchange Commission (the “SEC”) under the Securities Act of 1933, as amended (the “Securities Act”), or ~~Bylaws;~~the ~~Change~~Exchange Act, regardless of any general incorporation language contained in ~~Fiscal~~such ~~Year~~filing, except as expressly set forth by specific reference in such a filing.

On July 24, 2025, Mersana Therapeutics, Inc. (the “Company”) filed a Certificate of Amendment to the Company’s Fifth Amended and Restated Certificate of Incorporation, as amended, (the “Certificate of Amendment”) with the Secretary of State of the State of Delaware, which will effect, as of 5:00 p.m. Eastern Time, on July 25, 2025 (the “Effective Time”), a 1-for-25 reverse stock split (the “Reverse Stock Split”) of the issued and outstanding shares of the Company’s common stock, $0.0001 par value per share (the “Common Stock”).

The Reverse Stock Split is intended, among other things, to bring the Company into compliance with the minimum bid price requirement for continued listing on the Nasdaq Global Select Market, as previously reported in the Company’s definitive proxy statement for the Company’s annual meeting of stockholders held on June 12, 2025, as filed with the Securities and Exchange Commission on April 29, 2025 (the “Proxy Statement”).

At the Effective Time, every twenty-five shares of issued and outstanding Common Stock will be automatically reclassified and combined into one share of Common Stock. No fractional shares will be issued in connection with the Reverse Stock Split. Stockholders who would otherwise be entitled to a fractional share of Common Stock are instead entitled to receive a cash payment in lieu of such fractional shares.

The Reverse Stock Split will not change the number of authorized shares of Common Stock or the par value of the Common Stock. Proportionate adjustments will be made to the number of shares of Common Stock available for issuance under the Company’s equity incentive plans, as well as the number of shares underlying, and the exercise prices of, outstanding equity awards under such plans, in accordance with their respective terms and as described in the Proxy Statement.

The Common Stock is expected to begin trading on a post-Reverse Stock Split basis at the market open on July 28, 2025 under the Company’s existing trading symbol “MRSN”. The new CUSIP number for the Common Stock following the Reverse Stock Split is 59045L205.

The foregoing description of the Certificate of Amendment does not purport to be complete and is qualified in its entirety by reference to the complete text of the Certificate of Amendment, a copy of which is attached hereto as Exhibit 3.1 and is incorporated herein by reference.

Item 9.01.

Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.	~~Description~~	Description
3.1	Certificate of Amendment to Fifth Amended and Restated Certificate of Incorporation, as amended, of Mersana Therapeutics, Inc.
99.1		Press Release issued by the Company on August 13, 2025.
104	~~Cover Page Interactive Data File (embedded within the Inline XBRL document).~~	Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURES

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.

	MERSANA THERAPEUTICS, INC.
Date: July 24, 2025	By:	/s/ Brian DeSchuytner
Date: August 13, 2025	By:	/s/ Brian DeSchuytner
		Brian DeSchuytner
		Senior Vice President, Chief Operating Officer and Chief Financial Officer

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