MRSN Stock Soars Over 200% Pre-Market After Day One Acquisition Deal

• Day One will purchase Mersana for a total consideration of up to $55.25 per share. 
• The transaction is expected to close by the end of January 2026, and Day One expects to finance it with existing cash resources. 
• The acquisition will add antibody-drug conjugate (ADC) emiltatug ledadotin (Emi-Le) to Day One’s cancer portfolio.

Day One Biopharmaceuticals, Inc. (DAWN) said on Thursday that it has signed a definitive merger agreement to acquire Mersana Therapeutics (MRSN) for up to $285 million to expand its oncology portfolio.

Brisbane-based Day One will commence a tender offer to acquire all of the outstanding shares of Mersana common stock for $25 per share in cash at closing, in addition to a contingent value right that allows holders to receive up to an aggregate of $30.25 per CVR upon the completion of certain milestones for a total consideration of up to $55.25 per share.

The upfront purchase price of $25 alone represents a premium of 182% from Mersana’s closing price on Wednesday. The transaction is expected to close by the end of January 2026, and Day One expects to finance it with existing cash resources.

MRSN shares traded 200% higher in the pre-market session at the time of writing while DAWN shares dropped 12%.

Expanding Its Oncology Portfolio

The acquisition will add antibody-drug conjugate (ADC) emiltatug ledadotin (Emi-Le) to Day One’s cancer portfolio. Emi-Le has demonstrated early anti-tumor activity in an ongoing early-stage study for an aggressive cancer called adenoid cystic carcinoma type-1.

Day One believes that Emi-Le is well-positioned for potential rapid development and commercialization and expects its financial profile to aid the development of it through potential approval with no additional financing.

How Did Stocktwits Users React?

On Stocktwits, retail sentiment around MRSN jumped from ‘bearish’ to ‘extremely bullish’ territory over the past 24 hours, while message volume rose from ‘low’ to ‘extremely high’ levels.

MRSN stock is down by 75% this year and by 87% over the past 12 months. Meanwhile, DAWN stock has lost 18% this year. 

Also See: Ford Gears Up For Wider BlueCruise Rollout Across Europe In 2026

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