In a dramatic move that reshapes the biopharma landscape, Day One Biopharmaceuticals revealed Thursday that it will acquire Mersana Therapeutics Inc., a clinical-stage oncology innovator, in a deal that could reach $285 million. The transaction, steered by Fenwick & West LLP for Day One and WilmerHale for Mersana, marks a decisive step in expanding the pediatric cancer–focused company’s therapeutic arsenal.
A Take-Private Deal With Big-Ticket Milestones
Under the agreement, Day One will buy Mersana for $25 per share upfront and up to $30.25 per share in additional cash if key clinical, developmental, and regulatory milestones are met. That structure reflects a $129 million equity value at closing, but with room to nearly double as breakthroughs unfold.
Mersana—backed by Bain Capital Life Sciences—specializes in antibody-drug conjugates aimed at cancers with few, if any, effective treatments. Its standout program is Emi-Le, a first-in-class monotherapy targeting a rare, aggressive cancer often originating in the salivary glands.
