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  6. Day One Acquires Mersana Therapeutics

M&A Deal Summary

Day One Acquires Mersana Therapeutics

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

Acquisition Highlights
  • 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.

M&A Deal Summary
Date 2025-11-13
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

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(S) 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 STATS #
Overall 1 of 1
Sector: Life Science M&A 1 of 1
Type: Merger M&A Deals 1 of 1
State: Massachusetts M&A 1 of 1
Country: United States M&A 1 of 1
Year: 2025 M&A 1 of 1
Size (of disclosed) 1 of 1
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