Hack Andrew A. F.

SEC source: 0000899243-22-000588 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 5,385,667

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCIP Life Sciences Associates, LP ("BCIPLS") and BCLS II Investco, LP ("BCLS II Investco" and, together with BCLS II and BCIPLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. As a result, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-22-000158 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 4,570,667

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCIP Life Sciences Associates, LP ("BCIPLS") and BCLS II Investco, LP ("BCLS II Investco" and, together with BCLS II and BCIPLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. As a result, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-034455 · doc4.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 1,891,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · kind: Each share of Series B Convertible Preferred Stock was convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and had no expiration date. The Series B Convertible Preferred Stock was not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 27, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 1,891 shares of Series B Convertible Preferred Stock into an aggregate of 1,891,000 shares of the Issuer's common stock.

F3 · derivative.expiration_date: Each share of Series B Convertible Preferred Stock was convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and had no expiration date. The Series B Convertible Preferred Stock was not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 27, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 1,891 shares of Series B Convertible Preferred Stock into an aggregate of 1,891,000 shares of the Issuer's common stock.

F3 · derivative.underlying_shares: Each share of Series B Convertible Preferred Stock was convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and had no expiration date. The Series B Convertible Preferred Stock was not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 27, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 1,891 shares of Series B Convertible Preferred Stock into an aggregate of 1,891,000 shares of the Issuer's common stock.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-034455 · doc4.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 8,415,000

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-034455 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 10,415,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · kind: Each share of Series B Convertible Preferred Stock was convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and had no expiration date. The Series B Convertible Preferred Stock was not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 27, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 1,891 shares of Series B Convertible Preferred Stock into an aggregate of 1,891,000 shares of the Issuer's common stock.

F3 · shares: Each share of Series B Convertible Preferred Stock was convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and had no expiration date. The Series B Convertible Preferred Stock was not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 27, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 1,891 shares of Series B Convertible Preferred Stock into an aggregate of 1,891,000 shares of the Issuer's common stock.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-032571 · doc4.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 1,891

Underlying: Common Stock · 2,249,000 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · kind: Each share of Series B Convertible Preferred Stock is convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and has no expiration date. The Series B Convertible Preferred Stock is not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 9, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 2,249 shares of Series B Convertible Preferred Stock into an aggregate of 2,249,000 shares of the Issuer's common stock.

F3 · derivative.expiration_date: Each share of Series B Convertible Preferred Stock is convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and has no expiration date. The Series B Convertible Preferred Stock is not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 9, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 2,249 shares of Series B Convertible Preferred Stock into an aggregate of 2,249,000 shares of the Issuer's common stock.

F3 · derivative.underlying_shares: Each share of Series B Convertible Preferred Stock is convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and has no expiration date. The Series B Convertible Preferred Stock is not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 9, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 2,249 shares of Series B Convertible Preferred Stock into an aggregate of 2,249,000 shares of the Issuer's common stock.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-032571 · doc4.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 8,524,000

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-032571 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 10,774,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · kind: Each share of Series B Convertible Preferred Stock is convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and has no expiration date. The Series B Convertible Preferred Stock is not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 9, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 2,249 shares of Series B Convertible Preferred Stock into an aggregate of 2,249,000 shares of the Issuer's common stock.

F3 · shares: Each share of Series B Convertible Preferred Stock is convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock and has no expiration date. The Series B Convertible Preferred Stock is not convertible if, as a result of such conversion, the holder, together with its affiliates, would beneficially own more than 9.99% of the total number of shares of the Issuer's common stock then issued and outstanding immediately after giving effect to the conversion. On August 9, 2021, the Bain Capital Life Sciences Entities converted an aggregate of 2,249 shares of Series B Convertible Preferred Stock into an aggregate of 2,249,000 shares of the Issuer's common stock.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-031627 · doc4.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Class A Common Stock · 2,693,014 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · derivative.exercise_price: Each share of the Issuer's Series B Preferred Stock automatically converted into 0.1858 shares of the Issuer's Class A Common Stock immediately prior to the closing of the Issuer's initial public offering.

F3 · price: Each share of the Issuer's Series B Preferred Stock automatically converted into 0.1858 shares of the Issuer's Class A Common Stock immediately prior to the closing of the Issuer's initial public offering.

F3 · derivative.exercise_date: Each share of the Issuer's Series B Preferred Stock automatically converted into 0.1858 shares of the Issuer's Class A Common Stock immediately prior to the closing of the Issuer's initial public offering.

F3 · derivative.expiration_date: Each share of the Issuer's Series B Preferred Stock automatically converted into 0.1858 shares of the Issuer's Class A Common Stock immediately prior to the closing of the Issuer's initial public offering.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. As a result, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-031627 · doc4.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 3,428,014

F4 · shares: On August 2, 2021, BCLS II Investco purchased 735,000 shares of the Issuer's Class A Common Stock at a price of $17.00 per share in the Issuer's initial public offering.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. As a result, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-031627 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 2,693,014

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · price: Each share of the Issuer's Series B Preferred Stock automatically converted into 0.1858 shares of the Issuer's Class A Common Stock immediately prior to the closing of the Issuer's initial public offering.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. As a result, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-030847 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 43,000

Underlying: Class A Common Stock · 43,000 shares

Expires 2031-07-28

F1 · derivative.exercise_date: The shares underlying this option vest over three years in equal monthly installments following July 28, 2021, subject to continued service to the Company through the applicable vesting date.

SEC source: 0000899243-21-023969 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 25,050

Underlying: Common Stock · 25,050 shares

Expires 2031-06-10

F1 · derivative.exercise_date: The option vests in full on the earlier of the first anniversary of the date of grant or the date of the 2022 Annual Meeting of Stockholders of Mersana Therapeutics, Inc.

SEC source: 0000899243-21-023297 · doc4.xml · derivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

Underlying: Common Stock · 2,916,250 shares

Expires 2022-02-12

F3 · kind: On June 10, 2021, the Bain Capital Life Sciences Entities sold warrants to purchase an aggregate of 2,916,250 shares of common stock of the Issuer for aggregate consideration of $11,839,914.

F3 · price: On June 10, 2021, the Bain Capital Life Sciences Entities sold warrants to purchase an aggregate of 2,916,250 shares of common stock of the Issuer for aggregate consideration of $11,839,914.

F1 · ownership.nature: Represents securities held directly by Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-021645 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 25,000

Underlying: Common Stock · 25,000 shares

Expires 2028-05-27

F1 · derivative.exercise_date: This option vests fully on the one-year anniversary of the date of grant, or May 28, 2022.

SEC source: 0000899243-21-002549 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 2,971

Underlying: Common Stock · 2,971 shares

Expires 2031-01-15

F1 · derivative.exercise_date: The option becomes exercisable in equal quarterly installments on the last day of each calendar quarter of 2021.

SEC source: 0000899243-21-001552 · doc4.xml · nonDerivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 3,695,667

F5 · price: The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $17.795 to $18.61, inclusive. The reporting person undertakes to provide to Mersana Therapeutics, Inc., any security holder of Mersana Therapeutics, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth herein.

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II, the "Bain Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of the BCLS II, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-001552 · doc4.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 3,620,667

F4 · price: The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $18.05 to $18.93, inclusive. The reporting person undertakes to provide to Mersana Therapeutics, Inc., any security holder of Mersana Therapeutics, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth herein.

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II, the "Bain Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of the BCLS II, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-21-001552 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 3,545,667

F3 · price: The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $17.94 to $18.78, inclusive. The reporting person undertakes to provide to Mersana Therapeutics, Inc., any security holder of Mersana Therapeutics, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth herein.

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II, the "Bain Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of the BCLS II, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0001209191-20-059068 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 14,000

Underlying: Common Stock · 14,000 shares

Expires 2030-11-16

F1 · derivative.exercise_date: Stock option shall vest in full (i.e., in single installment) upon the earlier to occur of the first anniversary of the date of grant or the date of the next annual meeting of shareholders.

SEC source: 0000899243-20-030340 · doc4.xml · derivative · entry 4

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Underlying: Common Stock · 1,982,469 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · derivative.exercise_price: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · price: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · derivative.exercise_date: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · derivative.expiration_date: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · derivative.underlying_shares: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F1 · ownership.nature: Represents shares held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco, and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-030340 · doc4.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Underlying: Common Stock · 3,383,190 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · derivative.exercise_price: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · price: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · derivative.exercise_date: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · derivative.expiration_date: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F3 · derivative.underlying_shares: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F1 · ownership.nature: Represents shares held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco, and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-030340 · doc4.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 5,615,659

F4 · shares: On November 3, 2020, BCLS II Investco purchased 250,000 shares of common stock of the Issuer at a price of $24.00 per share, pursuant to an underwritten public offering.

F1 · ownership.nature: Represents shares held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco, and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-030340 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 5,365,659

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · price: The preferred stock was convertible at any time, at the holder's election and had no expiration date. Each share of preferred stock was automatically converted into one share of common stock upon the closing of the Issuer's initial public offering of its common stock.

F1 · ownership.nature: Represents shares held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), BCLS II Investco, LP ("BCLS II Investco") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the ultimate general partner of each of BCLS II and BCLS II Investco, and (ii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-029945 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 80,000

Underlying: Common Stock · 80,000 shares

Expires 2030-10-28

F1 · derivative.exercise_date: The option vests and becomes exercisable in 36 equal monthly installments following October 29, 2020.

SEC source: 0000899243-20-029242 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director · Chief Financial Officer · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 487,500

F1 · kind: The reported Class A ordinary shares were purchased from the Issuer in a private placement by BCLS Acquisition Holdings, LP (the "Sponsor") for $10.00 per share, as described in the Issuer's registration statement on Form S-1 (File No. 333-249284).

F2 · ownership.nature: The shares are held by the Sponsor. The Sponsor is controlled by its general partner, BCLS Acquisition Holdings (GP), LLC (the "General Partner"), which is governed by a board of managers consisting of three managers. Each manager has one vote, and the approval of a majority of the managers is required to approve an action on behalf of the Sponsor. Andrew Hack serves on the board of managers of the General Partner. As a result, Dr. Hack may be deemed to share beneficial ownership of the shares held by the Sponsor. Dr. Hack disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein.

SEC source: 0001209191-20-039303 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 9,200

Underlying: Common Stock · 9,200 shares

Expires 2030-06-25

F1 · derivative.exercise_date: The option vests in full on the earlier of the first anniversary of the date of grant or the date of the 2021 Annual Meeting of Stockholders of Mersana Therapeutics, Inc.

SEC source: 0000899243-20-014556 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 18,750

Underlying: Common Stock · 18,750 shares

Expires 2027-05-27

F2 · price: Not applicable.

F1 · derivative.exercise_date: This option vests fully on May 28, 2021, on the one year anniversary of the grant.

SEC source: 0000899243-20-014431 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 8,525,000

F1 · kind: On May 27, 2020, Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, collectively with BCLS, the "Bain Life Sciences Entities") purchased, in the aggregate, 1,000,000 shares of common stock of the Issuer at a price of $5.00 per share, pursuant to an underwritten public offering.

F2 · ownership.nature: Represents shares of common stock held directly by the Bain Life Sciences Entities.

F3 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-010592 · doc4.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 3,445,667

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II, the "Bain Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of the BCLS II, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-010592 · doc4.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 2,800,000

F1 · ownership.nature: Represents shares of common stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS II") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II, the "Bain Life Sciences Entities").

F2 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of the BCLS II, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-20-008067 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 1

Underlying: Preferred Warrants(Right to Buy) · 2,916.25 shares

Expires 2022-02-12

F1 · derivative.exercise_price: On March 11, 2020, each of Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Life Sciences Entities") entered into a letter agreement with the Issuer that provides the Bain Life Sciences Entities with the right, on one occasion, to exchange all or any portion of the warrants to purchase an aggregate of 2,916,250 shares of the Issuer's common stock (each, a "Warrant") owned by the Bain Life Sciences Entities for one or more warrants (each, a "Preferred Warrant") to purchase shares of the Issuer's non-voting Series C Convertible Preferred Stock (the "Series C Preferred Stock"). Each share of Series C Preferred Stock will be convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock.

F2 · derivative.exercise_price: (Continued from footnote 1) Each Preferred Warrant issued in exchange for a Warrant will have an exercise price of $4,500 per share of Series C Preferred Stock and will be exercisable for a number of shares of Series C Preferred Stock equal to (x) the number of shares of Common Stock for which the Warrant then remains exercisable, divided by (y) 1,000. The Warrants, the Series C Preferred Stock and the Series B Convertible Preferred Stock held by the Bain Life Sciences Entities each include provisions prohibiting exercise or conversion into the Issuer's common stock to the extent such exercise or conversion would result in beneficial ownership of the Issuer's common stock in excess of 9.99%.

F1 · shares: On March 11, 2020, each of Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Life Sciences Entities") entered into a letter agreement with the Issuer that provides the Bain Life Sciences Entities with the right, on one occasion, to exchange all or any portion of the warrants to purchase an aggregate of 2,916,250 shares of the Issuer's common stock (each, a "Warrant") owned by the Bain Life Sciences Entities for one or more warrants (each, a "Preferred Warrant") to purchase shares of the Issuer's non-voting Series C Convertible Preferred Stock (the "Series C Preferred Stock"). Each share of Series C Preferred Stock will be convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock.

F2 · shares: (Continued from footnote 1) Each Preferred Warrant issued in exchange for a Warrant will have an exercise price of $4,500 per share of Series C Preferred Stock and will be exercisable for a number of shares of Series C Preferred Stock equal to (x) the number of shares of Common Stock for which the Warrant then remains exercisable, divided by (y) 1,000. The Warrants, the Series C Preferred Stock and the Series B Convertible Preferred Stock held by the Bain Life Sciences Entities each include provisions prohibiting exercise or conversion into the Issuer's common stock to the extent such exercise or conversion would result in beneficial ownership of the Issuer's common stock in excess of 9.99%.

F1 · derivative.underlying_shares: On March 11, 2020, each of Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Life Sciences Entities") entered into a letter agreement with the Issuer that provides the Bain Life Sciences Entities with the right, on one occasion, to exchange all or any portion of the warrants to purchase an aggregate of 2,916,250 shares of the Issuer's common stock (each, a "Warrant") owned by the Bain Life Sciences Entities for one or more warrants (each, a "Preferred Warrant") to purchase shares of the Issuer's non-voting Series C Convertible Preferred Stock (the "Series C Preferred Stock"). Each share of Series C Preferred Stock will be convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock.

F2 · derivative.underlying_shares: (Continued from footnote 1) Each Preferred Warrant issued in exchange for a Warrant will have an exercise price of $4,500 per share of Series C Preferred Stock and will be exercisable for a number of shares of Series C Preferred Stock equal to (x) the number of shares of Common Stock for which the Warrant then remains exercisable, divided by (y) 1,000. The Warrants, the Series C Preferred Stock and the Series B Convertible Preferred Stock held by the Bain Life Sciences Entities each include provisions prohibiting exercise or conversion into the Issuer's common stock to the extent such exercise or conversion would result in beneficial ownership of the Issuer's common stock in excess of 9.99%.

F1 · balance_after: On March 11, 2020, each of Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Life Sciences Entities") entered into a letter agreement with the Issuer that provides the Bain Life Sciences Entities with the right, on one occasion, to exchange all or any portion of the warrants to purchase an aggregate of 2,916,250 shares of the Issuer's common stock (each, a "Warrant") owned by the Bain Life Sciences Entities for one or more warrants (each, a "Preferred Warrant") to purchase shares of the Issuer's non-voting Series C Convertible Preferred Stock (the "Series C Preferred Stock"). Each share of Series C Preferred Stock will be convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock.

F2 · balance_after: (Continued from footnote 1) Each Preferred Warrant issued in exchange for a Warrant will have an exercise price of $4,500 per share of Series C Preferred Stock and will be exercisable for a number of shares of Series C Preferred Stock equal to (x) the number of shares of Common Stock for which the Warrant then remains exercisable, divided by (y) 1,000. The Warrants, the Series C Preferred Stock and the Series B Convertible Preferred Stock held by the Bain Life Sciences Entities each include provisions prohibiting exercise or conversion into the Issuer's common stock to the extent such exercise or conversion would result in beneficial ownership of the Issuer's common stock in excess of 9.99%.

F1 · ownership.nature: On March 11, 2020, each of Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS, the "Bain Life Sciences Entities") entered into a letter agreement with the Issuer that provides the Bain Life Sciences Entities with the right, on one occasion, to exchange all or any portion of the warrants to purchase an aggregate of 2,916,250 shares of the Issuer's common stock (each, a "Warrant") owned by the Bain Life Sciences Entities for one or more warrants (each, a "Preferred Warrant") to purchase shares of the Issuer's non-voting Series C Convertible Preferred Stock (the "Series C Preferred Stock"). Each share of Series C Preferred Stock will be convertible, at the option of the holder, into 1,000 shares of the Issuer's common stock.

F2 · ownership.nature: (Continued from footnote 1) Each Preferred Warrant issued in exchange for a Warrant will have an exercise price of $4,500 per share of Series C Preferred Stock and will be exercisable for a number of shares of Series C Preferred Stock equal to (x) the number of shares of Common Stock for which the Warrant then remains exercisable, divided by (y) 1,000. The Warrants, the Series C Preferred Stock and the Series B Convertible Preferred Stock held by the Bain Life Sciences Entities each include provisions prohibiting exercise or conversion into the Issuer's common stock to the extent such exercise or conversion would result in beneficial ownership of the Issuer's common stock in excess of 9.99%.

F3 · ownership.nature: Bain Capital Life Sciences Investors, LLC ("BCLSI") is the ultimate general partner of BCLS, and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. Dr. Hack is a Managing Director of BCLSI. By virtue of the relationships described in this footnote, Dr. Hack may be deemed to share voting and dispositive power with respect to the securities held by the Bain Life Sciences Entities. Dr. Hack disclaims beneficial ownership of such securities except to the extent of his pecuniary interest therein.

SEC source: 0000899243-19-021741 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 15,000

Underlying: Common Stock · 15,000 shares

Expires 2026-08-11

F2 · price: Not applicable.

F1 · derivative.exercise_date: This option grant will vest over three years in equal installments on the anniversary of the grant date.

SEC source: 0001104659-19-034780 · a4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 25,000

Underlying: Common Stock · 25,000 shares

Expires 2029-06-07

F1 · derivative.exercise_date: The option vests in full on the earlier of the first anniversary of the date of grant or the date of the 2020 Annual Meeting of Stockholders of Mersana Therapeutics, Inc.

SEC source: 0001209191-19-035389 · doc4.xml · derivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 14,000

Underlying: Common Stock · 14,000 shares

Expires 2029-06-04

F1 · derivative.exercise_date: Stock option shall vest in full (i.e., in single installment) upon the earlier to occur of the first anniversary of the date of grant or the date of the next annual meeting of shareholders.

SEC source: 0001179110-19-001436 · edgar.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 9,618

Underlying: Common Stock · 6,895 shares

Expires 2025-09-13

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on September 28, 2018.

F3 · derivative.exercise_date: This option was granted on September 14, 2015 and is scheduled to vest over four years with 25% of the shares having vested on July 1, 2016, and the remaining 75% of the shares scheduled to vest in equal monthly installments thereafter through July 1, 2019.

SEC source: 0001179110-19-001436 · edgar.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on September 28, 2018.

F2 · price: This transaction was executed in multiple trades at prices ranging from $21.16 to $21.805. The price reported above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

SEC source: 0001179110-19-001436 · edgar.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 6,895

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on September 28, 2018.

SEC source: 0001179110-19-000578 · edgar.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 16,513

Underlying: Common Stock · 7,000 shares

Expires 2025-09-13

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F3 · derivative.exercise_date: This option was granted on September 14, 2015 and is scheduled to vest over four years with 25% of the shares having vested on July 1, 2016, and the remaining 75% of the shares scheduled to vest in equal monthly installments thereafter through July 1, 2019.

SEC source: 0001179110-19-000578 · edgar.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F2 · price: This transaction was executed in multiple trades at prices ranging from $22.08 to $22.80. The price reported above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

SEC source: 0001179110-19-000578 · edgar.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 7,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

SEC source: 0001179110-18-013245 · edgar.xml · derivative · entry 4

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 12,229

Underlying: Common Stock · 5,284 shares

Expires 2025-09-13

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F3 · derivative.exercise_date: This option was granted on September 14, 2015 and is scheduled to vest over four years, with 25% of the shares having vested on July 1, 2016, and the remaining 75% of the shares scheduled to vest in equal monthly installments thereafter through July 1, 2019.

SEC source: 0001179110-18-013245 · edgar.xml · nonDerivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

SEC source: 0001179110-18-013245 · edgar.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 100

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F2 · price: This transaction was executed in multiple trades at prices ranging from $27.48 to $28.41. The price reported above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected

SEC source: 0001179110-18-013245 · edgar.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 5,284

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

SEC source: 0001179110-19-000576 · edgar.xml · derivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 119,143

Underlying: Common Stock · 5,284 shares

Expires 2025-07-13

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · security: The Reporting Person is filing this amended Form 4 to amend the Form 4 filed by the Reporting Person with the SEC on November 27, 2018, which inadvertently reported the exercise of a different stock option held by the Reporting Person. This amended Form 4 now reflects the correct information regarding the option that was exercised.

F2 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F3 · derivative.exercise_date: This option was granted on July 14, 2015 and is scheduled to vest over four years with 25% of the shares having vested on July 1, 2016, and the remaining 75% of the shares scheduled to vest in equal monthly installments thereafter through July 1, 2019.

SEC source: 0001179110-19-000576 · edgar.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 5,284

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · security: The Reporting Person is filing this amended Form 4 to amend the Form 4 filed by the Reporting Person with the SEC on November 27, 2018, which inadvertently reported the exercise of a different stock option held by the Reporting Person. This amended Form 4 now reflects the correct information regarding the option that was exercised.

F2 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

SEC source: 0001179110-18-012390 · edgar.xml · derivative · entry 3

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 17,513

Underlying: Common Stock · 6,000 shares

Expires 2025-09-13

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F3 · derivative.exercise_date: This option was granted on September 14, 2015 and is scheduled to vest over four years, with 25% of the shares having vested on July 1, 2016, and the remaining 75% of the shares scheduled to vest in equal monthly installments thereafter through July 1, 2019.

SEC source: 0001179110-18-012390 · edgar.xml · nonDerivative · entry 2

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.

F2 · price: This transaction was executed in multiple trades at prices ranging from $25.20 to $26.19. The price reported above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

SEC source: 0001179110-18-012390 · edgar.xml · nonDerivative · entry 1

Hack Andrew A. F. · CIK 0001657434 · Chief Financial Officer

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 6,000

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · kind: The exercise and sale reported on this Form 4 were effected pursuant to a Rule 10b5-1 plan adopted by the Reporting Person on June 29, 2018.