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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
SCHEDULE 13G
Under the Securities Exchange Act of 1934
(Amendment No.             )*
Mersana Therapeutics, Inc.
(Name of Issuer)
Common Stock, par value $0.0001 per share
(Title of Class of Securities)
59045L106
(CUSIP Number)
January 15, 2021
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
☐ Rule 13d-1(b)
☒ Rule 13d-1(c)
☐ Rule 13d-1(d)
*
The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.
The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).
1

CUSIP No. 59045L106
 
  
 
13G
 
  
 
Page 2 of 8 Pages

1.
NAMES OF REPORTING PERSONS

Sarissa Capital Management LP
2.
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
 
(a)   ☐       (b)  ☐
3.
SEC USE ONLY
4.
CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH
5.
SOLE VOTING POWER

3,770,000
6.
SHARED VOTING POWER

0
7.
SOLE DISPOSITIVE POWER

3,770,000
8.
SHARED DISPOSITIVE POWER

0
9.
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

3,770,000
10.
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)  ☐
 
11.
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.5%(1)
12.
TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

PN
(1)
Calculations are based upon 68,497,425 Shares outstanding as of November 4, 2020, as set forth in the Form 10-Q of the Issuer filed with the U.S. Securities and Exchange Commission on November 9, 2020.
2

CUSIP No. 59045L106
 
  
 
13G
 
  
 
Page 3 of 8 Pages

1.
 NAMES OF REPORTING PERSONS

Alexander J. Denner, Ph.D.
2.
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)

(a)  ☐        (b)  ☐
3.
 
SEC USE ONLY
4.
CITIZENSHIP OR PLACE OF ORGANIZATION

United States
NUMBER OF
SHARES
 BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH 
5.
SOLE VOTING POWER

0
6.
SHARED VOTING POWER

3,770,000
7.
SOLE DISPOSITIVE POWER

0
8.
SHARED DISPOSITIVE POWER
3,770,000
9.
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

3,770,000
10.
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)  ☐
 
11.
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.5%(1)
12.
TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

IN
(1)
Calculations are based upon 68,497,425 Shares outstanding as of November 4, 2020, as set forth in the Form 10-Q of the Issuer filed with the U.S. Securities and Exchange Commission on November 9, 2020.

3

Item 1(a).
Name of Issuer:
Mersana Therapeutics, Inc. (the “Issuer”)
Item 1(b).
Address of Issuer’s Principal Executive Offices:
840 Memorial Drive, Cambridge, Massachusetts 02139
Item 2(a).
Name of Person Filing:
The persons filing this statement are Sarissa Capital Management LP, a Delaware limited partnership (“Sarissa Capital”) and Alexander J. Denner, Ph.D., a citizen of the United States of America (collectively, the “Reporting Persons”).
Item 2(b).
Address of Principal Business Office or, if None, Residence:
The principal business address of (i) each of Sarissa Capital and Dr. Denner is c/o Sarissa Capital Management LP, 660 Steamboat Road, Greenwich, CT 06830.
Item 2(c).
Citizenship:
See Item 2(a).
Item 2(d).
Title of Class of Securities:
Common Stock, $0.0001 par value per share (“Shares”).
Item 2(e).
CUSIP Number:
59045L106
Item 3.
If this statement is filed pursuant to Rule 13d-1(b) or Rule 13d-2(b) or (c), check whether the person filing is a:
Not applicable.
Item 4.
Ownership.
The information required by Items 4(a)-(c) is set forth in Rows 5-11 of the cover pages hereto for each Reporting Person and is incorporated herein by reference for each such Reporting Person.
Sarissa Capital has sole voting power and sole dispositive power with regard to 3,770,000 Shares.  By virtue of his position as the Chief Investment Officer of Sarissa Capital, Dr. Denner may be deemed to have the shared power to vote or direct the vote of (and the shared power to dispose or direct the disposition of) the 3,770,000 Shares over which Sarissa Capital has sole voting power and sole dispositive power.
Item 5.
Ownership of Five Percent or Less of a Class.
Not applicable.
4
Item 6.
Ownership of More than Five Percent on Behalf of Another Person.
Not applicable.

Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company.
Not applicable.
Item 8.
Identification and Classification of Members of the Group.
The Reporting Persons are making this single, joint filing because they may be deemed to constitute a “group” within the meaning of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). The agreement among the Reporting Persons to file jointly in accordance with Rule 13d-1(k) of the Exchange Act is attached hereto as Exhibit 99.1. The Reporting Persons disclaim membership in a group and this report shall not be deemed an admission by any of the Reporting Persons that they are or may be members of a “group” for purposes of Rule 13d-5 or for any other purpose.
Item 9.
Notice of Dissolution of Group.
Not applicable.
Item 10.
Certification.
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
5
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated:  January 25, 2021

SARISSA CAPITAL MANAGEMENT LP


By:         /s/ Mark DiPaolo                                   
 Name: Mark DiPaolo
 Title: Senior Partner and General Counsel



/s/Alexander J. Denner                       
Alexander J. Denner









EXHIBIT INDEX
 
     
   
Exhibit 99.1
  
Joint Filing Agreement, as required by Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended





7
Exhibit 99.1

JOINT FILING AGREEMENT

In accordance with Rule 13d−1(k)(1) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of Mersana Therapeutics, Inc. and further agree that this Joint Filing Agreement be included as an Exhibit to such joint filings. In evidence thereof, the undersigned, being duly authorized, have executed this Joint Filing Agreement this 25th day of January, 2021.



SARISSA CAPITAL MANAGEMENT LP

By:
/s/ Mark DiPaolo                         
  
 
Name: Mark DiPaolo
  
 
Title: Senior Partner and General Counsel
  

/s/Alexander J. Denner                                    
Alexander J. Denner