Day One Biopharmaceuticals Acquires Mersana Therapeutics in $285 Million Deal, Expanding ADC Portfolio
Day One Biopharmaceuticals has announced the acquisition of Mersana Therapeutics in a deal valued at up to $285 million, significantly bolstering its antibody-drug conjugate (ADC) pipeline. The agreement, which comes after Mersana's strategic restructuring earlier this year, centers around the promising B7-H4-targeted ADC, emiltatug ledadotin (Emi-Le).
Deal Structure and Financial Terms
Under the terms of the agreement, Day One will pay $25 per share in cash upfront, representing an equity value of approximately $129 million. This offer represents a substantial 180% premium over Mersana's closing stock price on the day before the announcement. Mersana shareholders are also eligible for additional contingent value rights of up to $30.25 per share, contingent upon Emi-Le achieving specific clinical, regulatory, and commercial milestones.
The total potential value of the deal could reach $285 million if all milestones are met. These include a $4 per share increase if Day One initiates a pivotal trial for Emi-Le in adenoid cystic carcinoma type 1 (ACC-1), $9 per share upon FDA approval, and further payments tied to additional approvals and annual sales targets of $300 million by 2037.
Strategic Rationale and Pipeline Focus
Day One CEO Jeremy Bender emphasized the strategic importance of the acquisition, stating, "This acquisition will add a potential game-changing new medicine to the Day One portfolio and, if approved, will broaden our opportunities for patient impact and for continued growth and value creation."
The primary asset driving this acquisition is Emi-Le, a dolasynthen ADC targeting B7-H4. While Mersana had been focusing on Emi-Le's potential in triple-negative breast cancer, Day One plans to prioritize its development for ACC-1, a rare and aggressive tumor type with limited treatment options. Day One believes that existing data may support a fast path to registration for this indication.
Clinical Development and Future Plans
Mersana has been conducting a phase 1 study of Emi-Le, with initial data presented earlier this year showing a 31% response rate in heavily pretreated patients. The expansion portion of this study in triple-negative breast cancer is ongoing.
Day One intends to leverage its existing research, development, and commercial capabilities to advance Emi-Le's development in ACC-1 and potentially other indications. The company sees an opportunity to address underserved, rare, and life-threatening cancers in patients of all ages.
The acquisition is expected to close by the end of January 2026, subject to customary closing conditions and regulatory approvals.
References
- Day One snaps up ADC maker Mersana in backloaded buyout deal
After multiple clinical setbacks and layoff rounds, Mersana accepted an offer in which the bulk of the payouts will only materialize if its main cancer drug hits a variety of milestones.
- Day One pens $285M deal for Mersana and its clinical-stage B7-H4 ADC
Mersana Therapeutics' decision earlier this year to go all-in on its antibody-drug conjugate Emi-Le appears to have paid off.
Explore Further
What are the key factors that influenced Day One Biopharmaceuticals' decision to prioritize Emi-Le's development for adenoid cystic carcinoma type 1 (ACC-1) over triple-negative breast cancer?
What sets Emi-Le apart from other antibody-drug conjugates targeting B7-H4 currently in development?
What is the competitive landscape for antibody-drug conjugates targeting rare tumor types like ACC-1, and who are the major players in this space?
What data or evidence suggests that Emi-Le could achieve a fast path to registration for ACC-1, and how does it compare to other therapies for this indication?
Are there notable companies or competitors pursuing similar acquisitions or partnerships in the area of antibody-drug conjugates or rare cancer treatments?