Mensana Therapeutics

Mersana Therapeutics was a Cambridge, Massachusetts-based clinical-stage oncology biotechnology company focused on antibody-drug conjugates. The company built a differentiated ADC platform portfolio that included Dolasynthen, Immunosynthen and the earlier Fleximer scaffold technologies, and it advanced wholly owned and partnered programs against validated and emerging tumor targets. Its lead internal program before acquisition was emiltatug ledadotin (Emi-Le; XMT-1660), a B7-H4-directed ADC in Phase 1 development for heavily pretreated triple-negative breast cancer and adenoid cystic carcinoma. Mersana also had partnered platform collaborations with Johnson & Johnson and Merck KGaA, and GSK held an exclusive global license option on XMT-2056, a HER2-directed STING agonist ADC. The company was acquired by Day One Biopharmaceuticals in January 2026.