US-based biopharmaceutical company Day One Biopharmaceuticals, Inc. (NASDAQ: DAWN) announced on Tuesday that it has completed its acquisition of Mersana Therapeutics, Inc. (NASDAQ: MRSN), expanding its oncology pipeline.

The deal adds emiltatug ledadotin, known as Emi-Le, a clinical-stage antibody drug conjugate targeting B7-H4 for adenoid cystic carcinoma, a rare cancer with no approved therapies.

Day One acquired all outstanding Mersana shares for USD25 per share in cash, plus one non-tradable contingent value right per share providing potential milestone payments of up to USD30.25, for total consideration of up to USD55.25 per share.

The tender offer expired on 5 January 2026, with 3,029,135 shares tendered, representing 60.57% of Mersana's outstanding shares and meeting the minimum condition for completion.

Following a statutory merger on 6 January 2026, Mersana became a wholly owned subsidiary of Day One, and all remaining shares were converted into the same cash and contingent value right consideration. Subsequently, Mersana's common stock ceased trading on the Nasdaq stock exchange and was delisted prior to market open on 6 January 2026.