Merger • Life Science

Day One Acquires Mersana Therapeutics

On November 13, 2025, Day One acquired life science company Mersana Therapeutics for 285M USD

Acquisition Context

This is Day One’s 1st transaction in the Life Science sector.
This is Day One’s largest (disclosed) transaction.
This is Day One’s 1st transaction in the United States.
This is Day One’s 1st transaction in Massachusetts.

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M&A Deal Summary
Date	November 13, 2025
Target	Mersana Therapeutics
Sector	Life Science
Buyer(s)	Day One
Deal Type	Merger
Deal Value	285M USD
Advisor(s)	Wilmer Cutler Pickering Hale and Dorr (Legal)

Target Company

Mersana Therapeutics

Cambridge, Massachusetts, United States

Mersana Therapeutics is a clinical stage biopharmaceutical company, develops antibody drug conjugates (ADC) for cancer patients with unmet need. Mersana Therapeutics was founded in 2001 and is based in Cambridge, Massachusetts.

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Buyer Overview 1

Buyer

Day One

South San Francisco, California, United States

Category	Company
Founded	2018
Sector	Life Science
Revenue	131M USD (2024)

DESCRIPTION

Day One is a clinical-stage biopharmaceutical company dedicated to developing and commercializing targeted therapies for patients of all ages with genetically defined cancers. Day One was founded in 2018 and is based in South San Francisco, California.

Deal Context for Buyer	#
Overall	1 of 1
Sector: Life Science	1 of 1
Type: Merger	1 of 1
State: Massachusetts	1 of 1
Country: United States	1 of 1
Year: 2025	1 of 1
Size (of disclosed)	1 of 1

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