Agreement with Day One Biopharmaceuticals provides for upfront consideration of $25.00 per share in cash, plus potential contingent value rights cash payments of up to an aggregate of $30.25 per share, for aggregate deal value of up to approximately $285 million
Closing is expected to occur by the end of January 2026
Mersana Therapeutics, a clinical-stage biopharmaceutical company focused on the development of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, announced that it has entered into a definitive merger agreement with Day One Biopharmaceuticals (“Day One”), pursuant to which Day One would acquire Mersana, through a tender offer followed by a second step merger, for upfront consideration of $25.00 per share in cash plus up to an aggregate of $30.25 per share in cash potentially payable under contingent value rights (“CVRs”) upon the achievement of certain clinical development, regulatory and commercial milestones related to Emi-Le, Mersana’s B7-H4-directed Dolasynthen ADC, and upon the achievement of a certain milestone pursuant to an existing Mersana collaboration to be issued in the proposed acquisition, representing a total equity value of approximately $129 million at closing and representing a total deal value of up to approximately $285 million. The Board of Directors of Mersana unanimously recommends that stockholders tender their shares in the Day One tender offer once it is commenced.
“We are excited that Day One, a company that creatively and intentionally develops new medicines for people of all ages with life-threatening diseases, recognizes the potential value created by Mersana. We believe this proposed acquisition recognizes the work that Mersana has done to develop Emi-Le and that the combination of Mersana’s assets and Day One’s research, development and commercial capabilities has the potential to bring more medicines to patients waiting for new therapies,” said Marty Huber, M.D., President and Chief Executive Officer of Mersana. “While Mersana has been focused on Emi-Le’s potential to treat patients with triple-negative breast cancer (TNBC) previously treated with topoisomerase-1 inhibitor ADCs, this transaction provides the near-term opportunity to support the development of Emi-Le for patients with adenoid cystic carcinoma, a population with very high unmet need.”
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Under the terms of the definitive merger agreement, the tender offer is required to be commenced within 10 business days of November 12, 2025. Any shares not tendered in the tender offer will be acquired in a second-step merger for the same consideration as paid in the tender offer on a per share of Mersana common stock basis. Closing of the transaction is subject to the satisfaction of customary closing conditions, including that a majority of Mersana’s shares of common stock are validly tendered in the tender offer and not validly withdrawn and the receipt of certain U.S. regulatory approvals. Upon the closing of the transaction, Mersana will become a wholly-owned subsidiary of Day One and shares of Mersana’s common stock will no longer be listed on any exchange.
The transaction was unanimously approved by the Mersana board of directors and closing is expected to occur by the end of January 2026. Mersana’s executive officers, directors and certain stockholders affiliated with Bain Capital Life Sciences, holding in the aggregate approximately 8.5% of Mersana’s outstanding shares of common stock, have signed tender and support agreements under which such stockholders agreed, among other things, to tender their shares in the tender offer.
TD Cowen is acting as financial advisor to Mersana. Wilmer Cutler Pickering Hale and Dorr LLP is acting as legal counsel to Mersana in connection with the transaction. Fenwick & West LLP is serving as legal counsel to Day One.
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