Day One Biopharmaceuticals announced a definitive agreement to acquire Mersana Therapeutics (Nasdaq: MRSN), marking a strategic move to strengthen its position in oncology drug development. The deal, valued at up to $285 million, combines Day One’s commercial expertise with Mersana’s innovative antibody-drug conjugate (ADC) technology, expanding the company’s pipeline in targeted cancer therapies.
Under the terms of the agreement, Day One will acquire Mersana through a tender offer followed by a merger, offering $25 per share in cash upfront and up to $30.25 per share in additional contingent value rights (CVRs). The CVRs are tied to the achievement of specific clinical, regulatory, and commercial milestones, particularly related to Emi-Le (emiltatug ledadotin), Mersana’s B7-H4-directed ADC candidate. The total equity value at closing is estimated at $129 million, with the full deal potentially reaching $285 million if all milestones are met.
The acquisition highlights Day One’s intent to broaden its oncology focus beyond its current lead programs. Known for its commitment to developing therapies for pediatric and underserved cancer populations, Day One plans to leverage Mersana’s ADC platforms—Dolasynthen and Immunosynthen—to accelerate the development of next-generation cancer treatments.
For Mersana, the deal represents both validation and a strategic exit amid a challenging biotech funding environment. The company has been recognized for its innovative ADC technology, which delivers cytotoxic and immune-modulating agents directly to cancer cells, minimizing harm to healthy tissue. Its lead candidate, Emi-Le, is currently being explored for the treatment of triple-negative breast cancer and adenoid cystic carcinoma, both areas with high unmet clinical needs.
Upon completion of the acquisition, Mersana will become a wholly owned subsidiary of Day One, and its common stock will be delisted from public exchanges. The transaction is expected to close by the end of January 2026, subject to customary regulatory approvals and the tender of a majority of Mersana’s outstanding shares.
The merger agreement was unanimously approved by Mersana’s board of directors, which has recommended that shareholders tender their shares once the offer is formally launched. Key shareholders, including affiliates of Bain Capital Life Sciences, representing approximately 8.5% of outstanding shares, have already agreed to support the transaction.
Financially, TD Cowen is serving as Mersana’s advisor, while WilmerHale is acting as legal counsel. Fenwick & West LLP is representing Day One in the deal.
This acquisition aligns with broader industry trends in oncology, where partnerships and mergers are accelerating innovation in targeted therapies. ADCs have become one of the most promising drug classes in oncology, combining precision targeting with potent efficacy. The addition of Mersana’s technology could give Day One a competitive edge in developing more effective, tumor-specific treatments.
With closing anticipated early next year, the merger positions Day One Biopharmaceuticals as a growing force in precision oncology, combining innovative science with a mission-driven focus on expanding treatment options for patients of all ages battling cancer.