EcoR1 Capital, LLC - Jul 27, 2023 Form 3 Insider Report for Mersana Therapeutics, Inc. (MRSN)

Role: 10%+ Owner
Signature: /s/ Oleg Nodelman
Stock symbol: MRSN
Transactions as of: Jul 27, 2023
Transactions value $: $0
Form type: 3
Date filed: 7/31/2023, 01:55 PM
Previous filing: Jun 21, 2023
Next filing: Oct 16, 2023

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
holding	MRSN	Common Stock						19.4M	Jul 27, 2023	See Notes 1 and 2	F1, F2

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	The filing persons (the "Filers") are EcoR1 Capital, LLC ("EcoR1"), Oleg Nodelman, and EcoR1 Capital Fund Qualified, L.P. ("Qualified Fund"). EcoR1 is the general partner and investment adviser of private funds, including Qualified Fund (collectively, the "Funds"). Mr. Nodelman is the manager and controlling owner of EcoR1. EcoR1 is filing this Form 3 for itself, Mr. Nodelman and Qualified Fund. The Filers are filing this Form 3 jointly, but not as a group, and each expressly disclaims membership in a group within the meaning of Rule 13d-5(b) under the Securities Exchange Act of 1934. The Funds hold these securities directly for the benefit of their investors. EcoR1 may be deemed to indirectly beneficially own them as the investment adviser to the Funds. Mr. Nodelman may be deemed to indirectly beneficially own them as the control person of EcoR1. The Filers disclaim beneficial ownership of the securities except to the extent of their respective pecuniary interests therein.
F2	Qualified Fund directly holds 18,260,899 of the shares of Common Stock reported in this Form 3.

Content

The filing persons (the "Filers") are EcoR1 Capital, LLC ("EcoR1"), Oleg Nodelman, and EcoR1 Capital Fund Qualified, L.P. ("Qualified Fund"). EcoR1 is the general partner and investment adviser of private funds, including Qualified Fund (collectively, the "Funds"). Mr. Nodelman is the manager and controlling owner of EcoR1. EcoR1 is filing this Form 3 for itself, Mr. Nodelman and Qualified Fund. The Filers are filing this Form 3 jointly, but not as a group, and each expressly disclaims membership in a group within the meaning of Rule 13d-5(b) under the Securities Exchange Act of 1934. The Funds hold these securities directly for the benefit of their investors. EcoR1 may be deemed to indirectly beneficially own them as the investment adviser to the Funds. Mr. Nodelman may be deemed to indirectly beneficially own them as the control person of EcoR1. The Filers disclaim beneficial ownership of the securities except to the extent of their respective pecuniary interests therein.

Qualified Fund directly holds 18,260,899 of the shares of Common Stock reported in this Form 3.