Martin H. Huber Jr. - Sep 11, 2025 Form 4 Insider Report for Mersana Therapeutics, Inc. (MRSN)

Role
President, CEO, Director
Signature
/s/ Alejandra Carvajal, Attorney-in-Fact
Stock symbol
MRSN
Transactions as of
Sep 11, 2025
Transactions value $
-$14,708
Form type
4
Date filed
9/15/2025, 04:26 PM
Previous filing
May 19, 2025
SEC
View on sec.gov

Reporting Owners (1)

Name Relationship Address Signature Signature date CIK
Huber Martin H. Jr. President, CEO, Director C/O MERSANA THERAPEUTICS, INC., 840 MEMORIAL DRIVE, CAMBRIDGE /s/ Alejandra Carvajal, Attorney-in-Fact 2025-09-15 0001653276

Transactions Table

Type Sym Class Transaction Value $ Shares Change % * Price $ Shares After Date Ownership Footnotes
transaction MRSN Common Stock Options Exercise $0 +6.67K +135.73% $0.00 11.6K Sep 11, 2025 Direct F1, F2
transaction MRSN Common Stock Sale -$14.7K -2.01K -17.37% $7.31 9.57K Sep 12, 2025 Direct F2, F3, F4

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type Sym Class Transaction Value $ Shares Change % * Price $ Shares After Date Underlying Class Amount Exercise Price Ownership Footnotes
transaction MRSN Restricted Stock Unit Options Exercise $0 -6.67K -33.33% $0.00 13.3K Sep 11, 2025 Common Stock 20K Direct F2, F5, F6
* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Buy Plan / Sale Plan: These are also open market purchases/sales of shares, but in this case the transaction is part of a trading plan. Rule 10b5-1 allows insiders to setup a trading plan to buy/sell stocks over a certain period of time. Since the purchases/sales are predetermined, this protects the insiders from violating insider trading law.

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).

Explanation of Responses:

Id Content
F1 Represents shares of common stock received upon vesting of a portion of the restricted stock units ("RSUs") awarded to the Reporting Person on September 11, 2023.
F2 Amounts reported in this Form 4 reflect the one-for-twenty-five reverse stock split effected by the Issuer on July 25, 2025.
F3 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 November 7, 2023. The sale was effected through an automatic "sell to cover" transaction that did not represent a discretionary trade by the Reporting Person.
F4 The price reported is a weighted average sales price. The shares were sold in multiple transactions at prices ranging from $7.22 to $7.31, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote.
F5 Each RSU represents the contingent right to receive one share of common stock of the Issuer.
F6 25% of the total number of RSUs granted vested on September 11, 2025, and the remainder shall vest thereafter in equal annual installments over the next two years.