| Item 1. | |
| (a) | Name of issuer:
Mersana Therapeutics, Inc. |
| (b) | Address of issuer's principal executive
offices:
840 Memorial Drive, Cambridge, MA 02139 |
| Item 2. | |
| (a) | Name of person filing:
EcoR1 Capital, LLC, a Delaware limited liability company ("EcoR1")
EcoR1 Capital Fund Qualified, L.P., a Delaware limited partnership ("Qualified Fund")
Oleg Nodelman
Qualified Fund is filing this statement jointly with the other reporting persons, but not as a member of a group, and it expressly disclaims membership in a group. In addition, the filing of this Schedule 13G on behalf of Qualified Fund should not be construed as an admission that it is, and it disclaims that it is, a beneficial owner, as defined in Rule 13d-3 under the Act, of any securities covered by this Schedule 13G. Each reporting person also disclaims beneficial ownership of the securities reported herein except to the extent of that person's pecuniary interest therein. |
| (b) | Address or principal business office or, if
none, residence:
357 Tehama Street #3
San Francisco, CA 94103 |
| (c) | Citizenship:
See Item 4 of the cover sheet for each reporting person. |
| (d) | Title of class of securities:
Common Stock |
| (e) | CUSIP No.:
59045L106 |
| Item 3. | If this statement is filed pursuant to §§
240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a: |
| (a) |  Broker
or dealer registered under section 15 of the Act (15 U.S.C. 78o); |
| (b) | Bank
as defined in section 3(a)(6) of the Act (15 U.S.C. 78c); |
| (c) | Insurance
company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c); |
| (d) | Investment
company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8); |
| (e) |  An
investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E); |
| (f) | An
employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F); |
| (g) | A
parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G); |
| (h) | A
savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C.
1813); |
| (i) | A
church plan that is excluded from the definition of an investment company under section 3(c)(14)
of the Investment Company Act of 1940 (15 U.S.C. 80a-3); |
| (j) | A
non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S.
institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please
specify the type of institution: |
| (k) | Group,
in accordance with Rule 240.13d-1(b)(1)(ii)(K). |
| | |
| Item 4. | Ownership |
| (a) | Amount beneficially owned:
EcoR1: 11,578,447
Qualified Fund: 10,918,474
Oleg Nodelman: 11,578,447 |
| (b) | Percent of class:
EcoR1: 9.99%
Qualified Fund: 9.4%
Oleg Nodelman: 9.99% % |
| (c) | Number of shares as to which the person has:
|
| | (i) Sole power to vote or to direct the vote:
EcoR1: 0
Qualified Fund: 0
Oleg Nodelman: 0
|
| | (ii) Shared power to vote or to direct the
vote:
EcoR1: 11,578,447
Qualified Fund: 10,918,474
Oleg Nodelman: 11,578,447
|
| | (iii) Sole power to dispose or to direct the
disposition of:
EcoR1: 0
Qualified Fund: 0
Oleg Nodelman: 0
|
| | (iv) Shared power to dispose or to direct the
disposition of:
EcoR1: 11,578,447
Qualified Fund: 10,918,474
Oleg Nodelman: 11,578,447
|
| Item 5. | Ownership of 5 Percent or Less of a Class. |
| | |
| Item 6. | Ownership of more than 5 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 or
Control Person. |
| |
Not Applicable
|
| Item 8. | Identification and Classification of Members
of the Group. |
| |
If a group has filed this schedule pursuant to §240.13d-1(b)(1)(ii)(J), so
indicate under Item 3(j) and attach an exhibit stating the identity and Item 3 classification of
each member of the group. If a group has filed this schedule pursuant to §240.13d-1(c) or
§240.13d-1(d), attach an exhibit stating the identity of each member of the group.
EcoR1 is the general partner and investment adviser of investment funds, including Qualified Fund. Mr. Nodelman is the control person of EcoR1. |
| Item 9. | Notice of Dissolution of Group. |
| |
Not Applicable
|
