Company: DAWN
Filing Date: 2025-11-13
Form Type: SC TO-C
Source: 0001104659-25-110833
Chunk: 1

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-11-13
Form: SC TO-C
Chunk 1
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4(i) (Cross-Border Issuer Tender Offer). |

| ¨ | Rule 14d-1(d) (Cross-Border Third-Party Tender Offer). |

This Tender Offer Statement
on Schedule TO relates solely to preliminary communications made before the commencement of a planned tender offer by Emerald Merger
Sub, Inc., a Delaware corporation (“Purchaser”) and wholly-owned subsidiary of Day One Biopharmaceuticals, Inc., a Delaware
corporation (“Day One”), for all of the outstanding shares of common stock of Mersana Therapeutics, Inc., a Delaware corporation
(“Mersana”), pursuant to the Agreement and Plan of Merger, dated as of November 12, 2025 (the “Merger Agreement”),
among Day One, Purchaser and Mersana.

Additional Information about the Transaction and Where to Find It

The tender offer described
in this communication (the “Offer”) has not yet commenced, and this communication is neither a recommendation, nor an offer
to purchase nor a solicitation of an offer to sell any shares of the common stock of Mersana or any other securities. On the commencement
date of the Offer, a tender offer statement on Schedule TO, including an Offer to Purchase, a Letter of Transmittal and related documents,
will be filed with the U.S. Securities and Exchange Commission (the “SEC”) by Day One and the Purchaser, and a Solicitation/Recommendation
Statement on Schedule 14D-9 will be filed with the SEC by Mersana. The offer to purchase shares of Mersana common stock will
only be made pursuant to the offer to purchase, the letter of transmittal and related documents filed as a part of the Schedule TO. INVESTORS
AND SECURITY HOLDERS ARE URGED TO READ BOTH THE TENDER OFFER STATEMENT AND THE SOLICITATION/RECOMMENDATION STATEMENT REGARDING THE OFFER,
AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT
INVESTORS AND SECURITY HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR COMMON STOCK, INCLUDING THE TERMS
AND CONDITIONS OF THE TENDER OFFER. Investors and security holders may obtain a free copy of these statements (when available) and other
documents filed with the SEC at Day One’s website at ir.dayonebio.com and (once they become available) will