Day One Biopharmaceuticals has concluded its acquisition of Mersana Therapeutics after meeting all the tender offer conditions.
The tender offer expired on 5 January 2026.
The transaction involved purchasing all outstanding shares of Mersana at $25 per share in cash, along with one non-tradable contingent value right (CVR) per share. The CVR entitles shareholders to potential milestone payments of up to $30.25 per CVR in cash.
The deal was first announced in November 2025 and had a total equity value of approximately $129m at closing, with the overall deal valued at up to $285m.
With this deal, Day One has incorporated a second new antibody-drug conjugate (ADC) into its clinical development pipeline.
Emi-Le (emiltatug ledadotin) is an advanced ADC directed against B7-H4, a known target in various cancers, including adenoid cystic carcinoma (ACC), which primarily affects salivary glands.
Following satisfaction of all conditions, Day One accepted these shares for payment. With the completion of a statutory merger under Section 251(h) of Delaware General Corporation Law on 6 January 2026, Mersana became Day One’s direct wholly owned subsidiary.
Day One CEO Jeremy Bender said: “This acquisition of Mersana is a strategic fit with Day One’s mission and ambitions, allowing us to continue to expand into adult oncology while maintaining a focus on rare cancers.
“With promising early clinical data, Emi-Le represents a potentially transformative advancement in the treatment of ACC, and we will leverage our distinct capabilities to rapidly develop the asset and pursue registration to reach patient communities who have no approved therapies today.”
“Building on the strong momentum of OJEMDA in the market and our continually progressing pipeline, this acquisition strengthens our overall position to expand our impact on patient communities while delivering sustainable business growth.”
In June 2024, Day One entered the field of ADCs through an exclusive licensing agreement with MabCare Therapeutics for its ADC MTX-13.
