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

1. Name and Address of Reporting Person* FMR LLC (Last) (First) (Middle) 245 SUMMER STREET (Street) BOSTON MA 02210 (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 Officer (give title below) X Other (specify below) See Remark 1
	3. Date of Earliest Transaction (Month/Day/Year) 07/03/2017
	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								383,357	I	F-Prime Capital Partners Healthcare Fund LP
Common Stock								2,597	I	F-Prime Capital Partners HC Principals Fund LP
Common Stock	07/03/2017		C		718,375	A	(1)	718,375	I	F-Prime Capital Partners Healthcare Fund III LP
Common Stock	07/03/2017		C		611,606	A	(1)	1,329,981	I	ccF-Prime Capital Partners Healthcare Fund III LP

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
Warrant	$0.05							09/27/2013	09/27/2023	Common Stock	19,126		19,126	I	F-Prime Capital Partners Healthcare Fund III LP
Series A-1 Convertible Preferred Stock	(1)	07/03/2017		C			718,375	(1)	(1)	Common Stock	718,375	(1)	0	I	F-Prime Capital Partners Healthcare Fund III LP
Series B-1 Convertible Preferred Stock	(1)	07/03/2017		C			611,606	(1)	(1)	Common Stock	611,606	(1)	0	I	F-Prime Capital Partners Healthcare Fund III LP

Explanation of Responses:

1. On July 3, 2017, in connection with the completion of the issuer's initial public offering, each share of Convertible Preferred Stock converted into one share of Common Stock.

Remarks:

Remark 1: Abigail P. Johnson is a Director, the Chairman and the Chief Executive Officer of FMR LLC. Members of the Johnson family, including Abigail P. Johnson, are the predominant owners, directly or through trusts, of Series B voting common shares of FMR LLC, representing 49% of the voting power of FMR LLC. The Johnson family group and all other Series B shareholders have entered into a shareholders' voting agreement under which all Series B voting common shares will be voted in accordance with the majority vote of Series B voting common shares. Accordingly, through their ownership of voting common shares and the execution of the shareholders' voting agreement, members of the Johnson family may be deemed, under the Investment Company Act of 1940, to form a controlling group with respect to FMR LLC. The address of Abigail P. Johnson is c/o FMR LLC, 245 Summer Street, Boston, MA 02110. Remark 2: The filing of this statement shall not be deemed to be an admission that, for purposes of Section 16 of the Securities Exchange Act of 1934 or otherwise, the undersigned are the beneficial owners of any securities reported herein. Remark 3: F-Prime Capital Partners Healthcare Advisors Fund III LP is the general partner of F-Prime Capital Partners Healthcare Fund III LP. F-Prime Capital Partners Healthcare Advisors Fund LP is the general partner of F-Prime Capital Partners Healthcare Fund LP and F-Prime Capital Partners HC Principals Fund LP. F-Prime Capital Partners Healthcare Advisors Fund III LP and F-Prime Capital Partners Healthcare Advisors Fund LP are solely managed by Impresa Management LLC, their general partner and investment manager. Impresa Management LLC is owned, directly or indirectly, by various shareholders and employees of FMR LLC, including certain members of the Johnson family.

	Marc R. Bryant, Duly authorized under Powers of Attorney, by and on behalf of FMR LLC and its direct and indirect subsidiaries, and Abigail P. Johnson	07/05/2017
	** Signature of Reporting Person	Date
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