Form 4: Mersana Director Exits Holdings Post-Merger

Mersana Therapeutics Director Anna Protopapas reports the disposition of all her company securities following the completion of its acquisition by Day One Biopharmaceuticals.

Summary

• Mersana Therapeutics, Inc. (MRSN) was acquired by Day One Biopharmaceuticals, Inc. through a merger agreement dated November 12, 2025.
• The merger became effective on January 6, 2026, at which point Mersana Therapeutics became a wholly-owned subsidiary of Day One Biopharmaceuticals.
• Shareholders received an Upfront Cash Consideration of $25.00 per share, plus one non-tradeable Contingent Value Right (CVR) per share.
• Each CVR represents the right to receive certain contingent milestone payments of up to an aggregate of $30.25 per CVR in cash.
• Anna Protopapas, a Director of Mersana Therapeutics, disposed of all her direct and indirect holdings of common stock, totaling 19,220 shares, as a result of the merger.
• Stock options with an exercise price less than the Upfront Cash Consideration (Cash-Out Options) became fully vested, cancelled, and converted into the Offer Price minus the exercise price.
• Stock options with an exercise price equal to or greater than the Upfront Cash Consideration (OTM Options) became fully vested and exercisable for a limited period, but those not exercised were cancelled without consideration.
• Following these transactions, Anna Protopapas no longer beneficially owns any Mersana Therapeutics securities and is no longer subject to Section 16 reporting requirements.

Sentiment

Score: 7

Explanation: The filing is a factual report of a completed merger transaction, resulting in the disposition of all securities by a director. It reflects the successful closing of the acquisition for shareholders who tendered their shares, but is neutral in terms of ongoing company performance.

Positives

• The merger successfully closed, providing Mersana Therapeutics shareholders with a defined cash payment and potential future contingent value rights.
• In-the-money stock options were cashed out, providing value to option holders.

Negatives

• Out-of-the-money stock options were cancelled without consideration if not exercised by the specified deadline.

Future Outlook

Mersana Therapeutics, Inc. is now a wholly-owned subsidiary of Day One Biopharmaceuticals, Inc. The future outlook for Mersana as an independent publicly traded entity is concluded. The realization of value from the Contingent Value Rights (CVRs) is dependent on the achievement of specified future milestones by Day One Biopharmaceuticals.

Industry Context

This announcement reflects a consolidation event within the biotechnology or pharmaceutical sector, where a smaller, publicly traded company (Mersana Therapeutics) is acquired by another entity (Day One Biopharmaceuticals). Such mergers are common strategies for larger companies to expand their pipeline or market share, and for smaller companies to gain resources or provide an exit for shareholders.

Management Changes

Corporate Governance

Stakeholder Impact

• Shareholders: Received cash and contingent value rights for their shares, concluding their investment in Mersana Therapeutics as an independent entity.
• Director (Anna Protopapas): Disposed of all holdings and is no longer subject to Section 16 reporting for Mersana, indicating a change in her relationship with the company post-merger.
• Mersana Therapeutics: Ceased to be an independent publicly traded company, becoming a subsidiary of Day One Biopharmaceuticals, Inc.

Next Steps

• Achievement of specified milestones by Day One Biopharmaceuticals, Inc. to trigger contingent payments for CVR holders.

Key Dates

Keywords

Mersana Therapeutics, Day One Biopharmaceuticals, Merger, Acquisition, Form 4, Beneficial Ownership, Stock Options, Contingent Value Right, Anna Protopapas