Mersana

Mersana Therapeutics, Inc. is a clinical-stage biopharmaceutical company based in Cambridge, Massachusetts that develops antibody-drug conjugates (ADCs) for cancers with unmet medical need. The company was incorporated in Delaware in 2001, initially under the name Nanopharma Corp., and adopted the Mersana Therapeutics name in November 2005. Its principal offices are at 840 Memorial Drive, Cambridge, MA 02139.

Mersana's work is built on its in-house Fleximer conjugation chemistry and derived platforms: Dolasynthen, used for cytotoxic ADCs, and Immunosynthen, used for immunostimulatory ADCs. Disclosed product candidates have included XMT-1592, a Dolasynthen ADC targeting NaPi2b-expressing tumor cells evaluated in Phase 1 for ovarian cancer and NSCLC adenocarcinoma; XMT-1660 (emiltatug ledadotin, "Emi-Le"), a Dolasynthen ADC directed against B7-H4; and XMT-2056, an Immunosynthen ADC targeting a novel epitope of HER2. Emi-Le is in clinical development for adenoid cystic carcinoma (ACC), a rare cancer usually arising in the salivary gland for which there are no approved therapies.

Mersana listed on Nasdaq under the ticker MRSN following a Form S-1 registration statement filed with the SEC on June 1, 2017 for an initial public offering underwritten by J.P. Morgan, Cowen, Leerink Partners and Wedbush PacGrow. In January 2026 Mersana was acquired by Day One Biopharmaceuticals and became a wholly owned subsidiary; its shares were delisted from Nasdaq.

Business model

Mersana develops proprietary ADC platforms and advances both wholly owned and partner-funded product candidates, combining internal pipeline development with strategic research and development collaborations that license its Fleximer conjugation technology to other pharmaceutical companies.

Revenue derives principally from strategic research and development collaborations built around its ADC platforms rather than from marketed products.

Traction

Mersana progressed multiple ADC candidates into clinical trials, including XMT-1592 in Phase 1 and XMT-1660/Emi-Le, which produced early clinical data in adenoid cystic carcinoma cited by Day One as a rationale for the acquisition. Employee headcount is reported in the 101-200 range.

Latest developments

Day One Biopharmaceuticals announced on November 13, 2025 that it would acquire Mersana, and completed the acquisition on January 6, 2026 at $25 per share in cash plus one non-tradable contingent value right per share worth up to $30.25, for total consideration of up to $55.25 per share. Holders tendered 3,029,135 shares, or 60.57% of outstanding shares, satisfying the minimum condition; Mersana became a wholly owned subsidiary and was delisted from Nasdaq. TD Cowen acted as Mersana's financial advisor and WilmerHale as its legal counsel. In March 2026, Servier and Day One announced an acquisition of Day One to expand Servier's rare oncology portfolio.