Day One Biopharmaceuticals agreed to acquire Mersana Therapeutics. This move will significantly expand its oncology portfolio with the addition of emiltatug ledadotin, also known as Emi-Le. The investigational antibody drug conjugate is being explored as a potential first-in-class monotherapy for adenoid cystic carcinoma type 1, a rare and aggressive cancer with limited therapeutic options and a highly unmet medical need.
The transaction underscores Day One’s plan to accelerate the development of innovative therapies for patients of all ages with life-threatening diseases. Emi-Le has demonstrated early anti-tumor activity in an ongoing Phase 1 study, targeting B7-H4, a well-characterized antigen highly expressed in ACC and other cancers across both adult and pediatric populations. The company believes the profile of Emi-Le, including its differentiated mechanism and potential for monotherapy benefit, positions the therapy for rapid advancement toward registration and future commercialization.
Day One plans to leverage its existing research, clinical development, and commercial infrastructure to support the advancement of Emi-Le. The company has stated that the acquisition strengthens its ability to develop therapies for patient groups with no approved options or established standards of care.
Under the terms of the merger agreement, Day One will launch a tender offer to purchase all outstanding shares of Mersana common stock for $25 per share in cash at closing, plus one non-tradable contingent value right per share. The CVR may deliver additional milestone-based payments of up to $30.25 per share, bringing the total potential payout to $55.25 per share. This reflects a total equity value of approximately $129 million at closing and as much as $285 million if all milestones are achieved.
Milestones tied to the CVR include development and regulatory achievements such as Breakthrough Therapy Designation for ACC granted by the FDA, first dosing in a registrational trial, and regulatory approval in the United States. Commercial milestones extend to first sales in major European markets and Japan, as well as tiered net sales thresholds up to more than $300 million by 2037.
Day One expects to fund the acquisition entirely with existing cash resources and does not anticipate the need for additional financing to take Emi-Le through potential approval. The company projects the transaction will close by the end of January 2026, pending regulatory reviews and other customary conditions.
Gordon Dyal & Co., LLC is serving as financial advisor to Day One, with Fenwick & West LLP acting as legal counsel. Mersana is being advised by TD Cowen and represented legally by Wilmer Cutler Pickering Hale and Dorr LLP.
KEY QUOTES:
“This acquisition will add a potential game-changing new medicine to the Day One portfolio and, if approved, will broaden our opportunities for patient impact and for continued growth and value creation.”
Jeremy Bender, Ph.D., Chief Executive Officer, Day One Biopharmaceuticals
“The addition of the Emi-Le program to our portfolio allows us to leverage the research and development expertise, and the commercial capabilities, that already exist within Day One to address underserved, rare and life-threatening cancers in patients of all ages.”
Jeremy Bender, Ph.D., Chief Executive Officer, Day One Biopharmaceuticals
