Mersana (NASDAQ: MRSN) sale pays $25 cash plus CVR per share

Rhea-AI Filing Summary

Mersana Therapeutics, Inc. completed its sale to Day One Biopharmaceuticals, Inc., with all tendered common shares exchanged for $25.00 in cash per share plus one contingent value right (CVR) per share. Each CVR represents potential milestone payments of up to an additional $30.25 in cash per CVR, subject to specified milestones and conditions. After the tender offer, Emerald Merger Sub, Inc. merged into Mersana on January 6, 2026, making Mersana a wholly owned subsidiary of Day One.

Options with exercise prices below the $25.00 upfront cash amount became fully vested and were cancelled in exchange for the Offer Price minus the option exercise price. Options with exercise prices at or above $25.00 were fully vested and exercisable for a limited period before the merger, and any such options not exercised by the last exercise date were cancelled at closing with no payment. Director Anna Protopapas reported exchanges of common shares, including shares held through family trusts for the benefit of her spouse and children, and the cancellation of multiple stock option awards in connection with these merger terms.

Insights

M&A and equity compensation analyst

Mersana’s sale locks in $25 cash plus CVR per share, with in-the-money options cashed out and out-of-the-money options cancelled.

The transactions show Mersana being acquired by Day One Biopharmaceuticals via a tender offer followed by a merger. Holders of common stock who tendered their shares receive an upfront $25.00 in cash per share plus one CVR, which may pay up to an additional $30.25 per CVR upon achievement of specified milestones. This structure combines immediate liquidity with future upside tied to milestone events defined in a contingent value rights agreement.

Equity awards are treated differently based on strike price. Options with exercise prices below $25.00 are fully vested, cancelled, and replaced with a cash-and-CVR payout equal to the Offer Price minus the strike, effectively monetizing intrinsic value. Options with exercise prices at or above $25.00 gain full vesting and a brief exercise window before closing, but any not exercised are cancelled with no consideration. For director Anna Protopapas, this results in reported cancellations of multiple stock option grants and the exchange of common shares, including shares held through family trusts, consistent with a full company sale and rollover of equity into cash and CVR claims.

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

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X

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

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Protopapas Anna

(Last) (First) (Middle)

C/O MERSANA THERAPEUTICS, INC.

840 MEMORIAL DRIVE

(Street)

CAMBRIDGE MA 02139

(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)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
01/06/2026

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	01/06/2026		U(1)(2)		6,721	D	(1)(2)	0	D
Common Stock	01/06/2026		U(1)(2)		2,890	D	(1)(2)	0	I	See footnote(5)
Common Stock	01/06/2026		U(1)(2)		9,609	D	(1)(2)	0	I	See footnote(6)

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
Stock Option (right to buy)	$9.0775	01/06/2026		D			2,460	(3)	(3)	Common Stock	2,460	(3)	0	D
Stock Option (right to buy)	$174.5	01/06/2026		D			2,500	(4)	(4)	Common Stock	2,500	(4)	0	D
Stock Option (right to buy)	$355.75	01/06/2026		D			480	(4)	(4)	Common Stock	480	(4)	0	D
Stock Option (right to buy)	$355.75	01/06/2026		D			7,519	(4)	(4)	Common Stock	7,519	(4)	0	D
Stock Option (right to buy)	$87.75	01/06/2026		D			542	(4)	(4)	Common Stock	542	(4)	0	D
Stock Option (right to buy)	$87.75	01/06/2026		D			8,137	(4)	(4)	Common Stock	8,137	(4)	0	D
Stock Option (right to buy)	$87.75	01/06/2026		D			1	(4)	(4)	Common Stock	1	(4)	0	D
Stock Option (right to buy)	$87.75	01/06/2026		D			18	(4)	(4)	Common Stock	18	(4)	0	D
Stock Option (right to buy)	$154	01/06/2026		D			988	(4)	(4)	Common Stock	988	(4)	0	D
Stock Option (right to buy)	$154	01/06/2026		D			11,761	(4)	(4)	Common Stock	11,761	(4)	0	D
Stock Option (right to buy)	$33	01/06/2026		D			665	(4)	(4)	Common Stock	665	(4)	0	D
Stock Option (right to buy)	$157	01/06/2026		D			9,043	(4)	(4)	Common Stock	9,043	(4)	0	D
Stock Option (right to buy)	$151.5	01/06/2026		D			11,250	(4)	(4)	Common Stock	11,250	(4)	0	D
Stock Option (right to buy)	$56.5	01/06/2026		D			2,200	(4)	(4)	Common Stock	2,200	(4)	0	D
Stock Option (right to buy)	$102.5	01/06/2026		D			1,131	(4)	(4)	Common Stock	1,131	(4)	0	D
Stock Option (right to buy)	$102.5	01/06/2026		D			5,227	(4)	(4)	Common Stock	5,227	(4)	0	D
Stock Option (right to buy)	$174.5	01/06/2026		D			166	(4)	(4)	Common Stock	166	(4)	0	D

Explanation of Responses:

1. Pursuant to the terms of that certain Agreement and Plan of Merger (the "Merger Agreement"), by and among the Issuer, Day One Biopharmaceuticals, Inc. ("Parent") and Parent's direct wholly-owned subsidiary, Emerald Merger Sub, Inc. ("Purchaser"), dated as of November 12, 2025, the shares (the "Shares") of common stock, par value $0.0001 per share, of the Issuer (the "Common Stock") that were tendered to Purchaser prior to the expiration time of the Offer were exchanged for: (i) $25.00 per Share, net to the stockholder in cash, without interest and less any applicable tax withholding (the "Upfront Cash Consideration"), plus (ii) one non-tradeable contingent value right per Share (each, a "CVR"),

2. (continued from footnote 1) which represents the right to receive certain contingent milestone payments of up to an aggregate of $30.25 per CVR in cash, without interest and less any applicable tax withholding, upon the achievement of certain specified milestones in accordance with the terms and subject to the conditions of a contingent value rights agreement entered into by Parent and the rights agent (the Upfront Cash Consideration plus one CVR, collectively, the "Offer Price"). After completion of the tender offer, pursuant to the terms of the Merger Agreement, Purchaser merged with and into the Issuer, effective as of January 6, 2026 (the "Effective Time"), with the Issuer continuing as the surviving corporation and a wholly owned subsidiary of Parent.

3. Pursuant to the terms of the Merger Agreement, effective as of immediately prior to the Effective Time, each option to purchase shares of Common Stock ("Issuer Option") that was outstanding and unexercised as of immediately prior to the Effective Time and had an exercise price per Share that was less than the Upfront Cash Consideration (each, a "Cash-Out Option"), became fully vested and was automatically cancelled and converted into the right to receive, without interest and subject to deduction for any required tax withholding, (i) the Offer Price minus (ii) the exercise price payable per share of Common Stock underlying such Cash-Out Option.

4. Pursuant to the terms of the Merger Agreement, effective as of 10 business days prior to the closing of the Merger (the "Acceleration Date"), each Issuer Option then outstanding and unexercised that had an exercise price per Share that was equal to or greater than the Upfront Cash Consideration (each, an "OTM Option"), became fully vested and exercisable up to and through the closing of regular trading on the Nasdaq Stock Market on the fifth business day following the Acceleration Date (the "Last Exercise Date"). OTM Options not exercised on or prior to the Last Exercise Date were cancelled and ceased to exist as of the Effective Time, and no consideration was delivered in exchange for such OTM Option.

5. These Shares were held by the Kinney/Protopapas Family Irrevocable Trust (the "Kinney/Protopapas Trust") for the benefit of the Reporting Person's children. The Reporting Person's spouse is a co-trustee of the Kinney/Protopapas Trust.

6. These Shares were held by the Anna Protopapas Irrevocable Trust (the "Protopapas Trust") for the benefit of the Reporting Person's spouse and children. The Reporting Person's spouse is the trustee of the Protopapas Trust.

	/s/ Anna Protopapas	01/06/2026
	** Signature of Reporting Person	Date
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FAQ

What happened to Mersana Therapeutics (MRSN) in this insider filing?

The content describes the completion of Mersana Therapeutics, Inc.’s sale to Day One Biopharmaceuticals, Inc. Common shares that were tendered in the offer were exchanged for $25.00 in cash per share plus one contingent value right (CVR) per share, and Mersana became a wholly owned subsidiary of Day One after the merger on January 6, 2026.

What consideration do Mersana (MRSN) shareholders receive in the merger?

Each tendered share of Mersana common stock is exchanged for $25.00 in cash, net of withholding and without interest, plus one non-tradeable CVR. Each CVR represents the right to receive contingent milestone payments of up to an aggregate of $30.25 in cash, subject to specified milestones and conditions set out in a contingent value rights agreement.

How were Mersana stock options treated in the Day One Biopharmaceuticals transaction?

Options with exercise prices below the $25.00 upfront cash amount became fully vested and were automatically cancelled in exchange for the Offer Price minus the option’s exercise price per share. Options with exercise prices equal to or above $25.00 became fully vested and exercisable for a limited period ending on the fifth business day after the acceleration date, and any such options not exercised by that last exercise date were cancelled at the merger closing with no consideration.

What did director Anna Protopapas report on this Form 4 for Mersana (MRSN)?

Director Anna Protopapas reported exchanges of common stock for the cash-and-CVR merger consideration and the disposition (cancellation) of multiple stock option awards in connection with the merger terms. Some of the common shares were held directly, while others were held indirectly through family trusts benefiting her spouse and children.

How do the contingent value rights (CVRs) work in the Mersana merger?

For each Mersana share exchanged, holders receive one CVR. Each CVR may pay up to an additional $30.25 in cash, without interest and net of any withholding, if specified milestones are achieved under a contingent value rights agreement between Day One Biopharmaceuticals and a rights agent. Payments, if any, depend on meeting those contractual milestones.

What is the role of the family trusts mentioned for Mersana director Anna Protopapas?

Certain reported Mersana shares were held by the Kinney/Protopapas Family Irrevocable Trust for the benefit of Anna Protopapas’s children, and by the Anna Protopapas Irrevocable Trust for the benefit of her spouse and children. Her spouse serves as co-trustee or trustee of these trusts, and the shares held in the trusts participated in the same cash-and-CVR exchange described in the merger terms.