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

Reporting relationship: President, CEO, Director
Issuer ticker: MRSN
Reported as of: 11 Sep 2025
Net transaction value: -$14,708
SEC form: 4
Accepted by SEC: 15 Sep 2025, 16:26:13 UTC
Prior SEC filing: 19 May 2025
Next SEC filing: 06 Jan 2026
Source filing: View source filing
Reporting owner signature: /s/ Alejandra Carvajal, Attorney-in-Fact

Key filing fact

Martin H. Huber Jr. filed Form 4 for Mersana Therapeutics, Inc. (MRSN) on 15 Sep 2025.

Key facts

This page summarizes Martin H. Huber Jr.'s Form 4 filing for Mersana Therapeutics, Inc. (MRSN).
3 reported transactions and 1 derivative row are listed below.
Accepted by SEC: 15 Sep 2025, 16:26.

Change

Previous filing in this sequence was filed on 19 May 2025.
Current net transaction value: -$14,708.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001653276 Primary reporting owner

Huber Martin H. Jr.

Relationship: President, CEO, Director
Address: C/O MERSANA THERAPEUTICS, INC., 840 MEMORIAL DRIVE, CAMBRIDGE
Signature: /s/ Alejandra Carvajal, Attorney-in-Fact
Signature date: 15 Sep 2025

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

MRSN transaction

Common Stock

Options Exercise

Transaction value: $0
Shares: +6,670
Change %: +136%
Price: $0.000000
Shares after: 11,584
Date: 11 Sep 2025
Ownership: Direct
Footnotes: F1, F2

MRSN transaction

Common Stock

Sale

Transaction value: $14,708
Shares: -2,012
Change %: -17%
Price: $7.31
Shares after: 9,572
Date: 12 Sep 2025
Ownership: Direct
Footnotes: F2, F3, F4

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

MRSN transaction Derivative

Restricted Stock Unit

Options Exercise

Transaction value: $0
Shares: -6,670
Change %: -33%
Price: $0.000000
Shares after: 13,340
Date: 11 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 20,010
Exercise price
Footnotes: F2, F5, F6

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Rule 10b5-1 trading plan

These transactions were reported as open-market trades under a Rule 10b5-1 plan. The plan lets an insider set trading instructions in advance, which can reduce the risk of trading while in possession of material nonpublic information.

Original filing language: transaction made pursuant to a contract, instruction, or written plan intended to satisfy Rule 10b5-1(c).

Explanation of responses 6 footnotes

Footnote 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.

Footnote F2

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

Footnote 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.

Footnote 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.

Footnote F5

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

Footnote 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.