Mersana Therapeutics (NASDAQ:MRSN) shares surged 200% on Thursday after Day One Biopharmaceuticals unveiled a takeover agreement that values the cancer drug developer at a steep premium. Day One plans to acquire Mersana for $25.00 per share in cash, a sharp jump from the company’s prior close of $8.87.
The transaction also includes additional contingent value rights (CVRs) that could deliver up to $30.25 per share in extra cash payments if a series of clinical, regulatory, and commercial milestones are met for Mersana’s B7-H4-targeting Dolasynthen ADC, Emi-Le. If fully realized, the deal carries a potential value of roughly $285 million.
Mersana — a clinical-stage biotech specializing in next-generation antibody-drug conjugates for cancer — will operate as a wholly owned subsidiary of Day One once the deal is finalized. Both companies expect the acquisition to close by January 2026, pending regulatory review and the successful completion of the tender offer.
“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,” said Marty Huber, M.D., President and CEO of Mersana.
The acquisition hands Day One access to Mersana’s development pipeline, anchored by Emi-Le, which is aimed at treating triple-negative breast cancer in patients previously treated with topoisomerase-1 inhibitor ADCs. The drug could also help speed progress in adenoid cystic carcinoma, an area marked by significant unmet need.
The tender offer will launch within 10 business days of November 12, 2025, and will require the majority of Mersana’s shares to be tendered. U.S. regulatory approvals are also required. Notably, about 8.5% of Mersana’s shares — held by executives, board members, and investors linked to Bain Capital Life Sciences — are already committed to the offer.