Mersana Therapeutics, Inc. (MRSN) entered a merger agreement on November 13, 2025, to be acquired by Day One Biopharmaceuticals, Inc. (DAWN) in a deal valued at $129 million.
Day One would acquire Mersana, through a tender offer, for upfront consideration of $25 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.
The upfront cash payment of $25 per share represents a premium of 181.85% from the stock’s last close.
Mersana Therapeutics is a clinical-stage biopharmaceutical company developing novel antibody-drug conjugates (ADCs) through its proprietary Dolasynthen and Immunosynthen platforms to create innovative cancer therapies for patients with unmet medical needs.
Day One Biopharmaceuticals is a commercial-stage biopharmaceutical company developing and commercializing targeted cancer therapies, including treatments for pediatric and genetically defined cancers, through its innovative pipeline led by tovorafenib (OJEMDA) and DAY301.
The closing of the deal is expected to occur by the end of January 2026.
Mersana’s certain stockholders affiliated with Bain Capital Life Sciences, collectively holding about 8.5% of the outstanding stock, have entered into tender and support agreements.
Mersana was advised by TD Cowen on financial matters and by WilmerHale on legal matters. Day One received legal advice from Fenwick & West.
More details on this M&A transaction can be found on the Deal Metrics page:
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– A spread history chart of the merger from announcement to completion or failure.
– Key events as the merger progresses, including HSR period expiration, regulatory approvals, shareholder votes, etc.
– News and SEC filings.
– A history of deal updates.
– And much more.
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Editor’s Note: Baranjot Kaur contributed to this article