Day One Biopharmaceuticals ( DAWN ) on Thursday agreed to acquire Mersana Therapeutics Inc. ( MRSN ) , a clinical-stage biopharmaceutical company focused on the development of antibody-drug conjugates (ADCs) targeting cancers.

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The deal value comprises an upfront consideration of $25.00 per share in cash plus up to an aggregate of $30.25 per share in cash potentially payable under contingent value rights, representing a total equity value of approximately $129 million and total deal value of up to roughly $285 million.

Day One is focused on pediatric cancers. The company’s pipeline includes tovorafenib (Ojemda) and DAY301.

In the third quarter, Ojemda’s net product revenue was $38.5 million compared to $20.1 million a year ago, driven by higher patient demand.

The company raised the Ojemda full-year 2025 net product revenue guidance to $145 to $150 million, reflecting continued strength in underlying demand.

Quarterly prescriptions (TRx) grew to 1,256 in the third quarter of 2025, representing an 18% increase compared to the second quarter of 2025.

Day One ended the third quarter with $451.6 million in cash, cash equivalents, and short-term investments.

“While Mersana has been focused on Emi-Le’s potential to treat patients with triple-negative breast cancer (TNBC) previously treated with topoisomerase-1 inhibitor ADCs, this transaction provides the near-term opportunity to support the development of Emi-Le for patients with adenoid cystic carcinoma, a population with very high unmet need,” said Marty Huber, President and CEO of Mersana.

The Mersana board unanimously approved the transaction of directors, and closing is expected to occur by the end of January 2026.

Price Action: Mersana Therapeutics ( MRSN ) shares were up 206.82% at $27.21 and Day One Biopharmaceutical shares were down 5.78% at $9.74 at the time of publication on Thursday, according to Benzinga Pro data.

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