[Form 4] Mersana Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Mersana Therapeutics (MRSN) insider activity: The SVP, Chief Development Officer reported RSU vesting of 250 shares of common stock on October 25, 2025, and an automatic sell-to-cover of 77 shares at $9.90 on October 27, 2025 under a Rule 10b5-1 trading plan adopted on May 10, 2023. Following these transactions, direct beneficial ownership is 2,922 shares.

The amounts reflect the one-for-twenty-five reverse stock split effected on July 25, 2025. Each RSU represented one common share, and the RSUs were fully vested as of October 25, 2025.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Bala Mohan

(Last) (First) (Middle)

C/O MERSANA THERAPEUTICS, INC.

840 MEMORIAL DRIVE

(Street)

CAMBRIDGE MA 02139

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Mersana Therapeutics, Inc. [ MRSN ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	SVP, Chief Development Officer

3. Date of Earliest Transaction (Month/Day/Year)
10/25/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	10/25/2025		M(1)		250(2)	A	$0	2,999(2)	D
Common Stock	10/27/2025		S(3)		77(2)	D	$9.9	2,922(2)	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Restricted Stock Unit	(4)	10/25/2025		M			250(2)	(5)	(5)	Common Stock	250(2)	$0	0(2)	D

Explanation of Responses:

1. Represents shares of common stock received upon vesting of the restricted stock units ("RSUs") awarded to the Reporting Person on October 25, 2021.

2. Amounts reported in this Form 4 reflect the one-for-twenty-five reverse stock split effected by the Issuer on July 25, 2025.

3. Represents the sale of shares of common stock to satisfy the Reporting Person's tax withholding obligations in connection with the service-based vesting and settlement of the RSUs pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on May 10, 2023. The sale was effected through an automatic "sell to cover" transaction that did not represent a discretionary trade by the Reporting Person.

4. Each RSU represents the contingent right to receive one share of common stock of the Issuer.

5. Fully vested as of October 25, 2025.

	/s/ Alejandra Carvajal, Attorney-in-Fact	10/28/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What insider transaction did MRSN report on Form 4?

The SVP, Chief Development Officer reported RSU vesting of 250 shares and an automatic sell-to-cover of 77 shares.

How many MRSN shares vested from RSUs and when?

250 shares vested on October 25, 2025; each RSU equaled one common share.

How many MRSN shares were sold to cover taxes and at what price?

77 shares were sold at $9.90 on October 27, 2025 to satisfy tax withholding.

Is the MRSN sale covered by a Rule 10b5-1 plan?

Yes. The sale was pursuant to a Rule 10b5-1 plan adopted on May 10, 2023 and executed as an automatic sell-to-cover.

What is the MRSN insider’s beneficial ownership after the transactions?

Direct beneficial ownership is 2,922 shares following the reported transactions.

Why do the MRSN share counts look adjusted?

Figures reflect the one-for-twenty-five reverse stock split effected on July 25, 2025.