Day One to acquire Mersana Therapeutics to advance mission to bring new medicines to people of all ages with life-threatening diseases

CAR-T Digest - August 2020

Weekly Digest - November 2025

13 November 2025: Day One to acquire Mersana Therapeutics to advance mission to bring new medicines to people of all ages with life-threatening diseases

Day One Biopharmaceuticals announced a major step in expanding its oncology portfolio by acquiring Mersana Therapeutics, bringing in the novel ADC emiltatug ledadotin (Emi-Le), which has already shown promising early anti-tumor activity in Phase 1 trials for adenoid cystic carcinoma type-1 (ACC-1)
The company sees Emi-Le, a B7-H4–targeted ADC, as a potential first-in-class monotherapy for adenoid cystic carcinoma a rare, aggressive cancer with no approved treatments giving it a clear and potentially rapid path toward registration
Day One highlighted that it will leverage its existing R&D and commercial strengths to accelerate the development and future commercialization of Emi-Le, aiming to bring a much-needed therapy to a patient population with high unmet need
The acquisition deal, valued at up to approximately $285 million, includes an upfront payment plus contingent value rights tied to key clinical, regulatory, and commercial milestones, reflecting confidence in Emi-Le’s long-term potential
With strong financial resources already in place, Day One expects to fund development through potential approval without additional financing, anticipating the transaction to close by January 2026 and positioning the company for continued growth