Day One Biopharmaceuticals has completed its acquisition of Mersana Therapeutics, marking a significant expansion of its oncology pipeline and reinforcing its strategy to advance targeted therapies for patients with rare and life-threatening cancers. The transaction closed after all conditions of Day One’s tender offer were satisfied, resulting in the purchase of all outstanding shares of Mersana.
Under the terms of the agreement, Mersana shareholders received $25 per share in cash, along with one non-tradable contingent value right (CVR) per share. Each CVR entitles holders to potential future milestone payments of up to an aggregate of $30.25 in cash, contingent on the achievement of specified development and regulatory milestones. The structure of the deal reflects Day One’s confidence in the scientific and clinical potential of Mersana’s assets while aligning long-term value creation with clinical success.
The acquisition is viewed as a strategic fit for Day One, which has historically focused on developing targeted therapies for pediatric patients and is now broadening its presence in adult oncology. According to Day One, the transaction strengthens its ability to address rare cancers with high unmet need, while also supporting sustainable business growth.
Jeremy Bender, Ph.D., chief executive officer of Day One Biopharmaceuticals, said the deal allows the company to expand its reach into adult oncology without losing focus on rare indications. He highlighted Emi-Le (emiltatug ledadotin), a novel antibody-drug conjugate (ADC) acquired through the transaction, as a potentially transformative therapy for adenoid cystic carcinoma (ACC). ACC is a rare and difficult-to-treat cancer that most commonly arises in the salivary glands and currently has no approved systemic therapies.
With the acquisition, Day One adds a second novel ADC to its clinical-stage pipeline. Emi-Le is designed to target B7-H4, a protein that is highly expressed in certain cancers, including ACC. B7-H4 is a well-characterized target that has attracted increasing interest due to its limited expression in normal tissues and its association with tumor growth and immune evasion. Early clinical data suggest Emi-Le may offer meaningful benefit for patients with few available treatment options.
Day One plans to leverage its development capabilities and regulatory expertise to advance Emi-Le rapidly through clinical development, with the goal of pursuing registration and making the therapy available to patients as quickly as possible. The company noted that this effort will build on the commercial momentum of OJEMDA, its approved therapy, as well as continued progress across its broader pipeline.
By integrating Mersana’s technology and assets, Day One aims to strengthen its position as a focused oncology company committed to delivering innovative treatments to underserved patient populations. The acquisition underscores the company’s long-term strategy of combining targeted science, disciplined development, and strategic transactions to expand its impact across both pediatric and adult oncology.