Company: DAWN
Filing Date: 2025-11-13
Form Type: SC TO-C
Source: 0001104659-25-110815
Chunk: 19

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-11-13
Form: SC TO-C
Chunk 19
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 pec ted financial performance of Mersana and its product candidates and the possibility that the milestone payments related to the contingent v alu e right will never be achieved and that no milestone payment may be made; the possibility that if Day One does not achieve the perceived bene fits of the proposed transaction as rapidly or to the extent anticipated by financial analysts or investors, the market price of Day One’ s s hares could decline; as well as other risks related to Day One’s and Mersana’s businesses detailed from time - to - time under the caption “Risk Factors” and elsewhere in Day One’s and Mersana’s respective SEC filings and reports, including their respective Annual Reports on Form 1 0 - K for the year ended December 31, 2024 and subsequent quarterly and current reports filed with the SEC. Day One undertakes no duty or o bli gation to update any forward - looking statements contained in this communication as a result of new information, future events or changes i n their expectations, except as required by law.

4 Agenda & Day One Participants Overview & Opportunity Jeremy Bender (Chief Executive Officer) Transaction Rationale Michael Vasconcelles (Head of R&D) Financial Overview & Transaction Details Charles York (Chief Operating & Chief Financial Officer) Q&A Session All Participants

Overview and Opportunity 5 Jeremy Bender Chief Executive Officer

A Compelling Opportunity Aligned With Our Mission 6 ACC, Adenoid Cystic Carcinoma. Emi - Le, Emiltatug Ledadotin The Emi - Le program strengthens our mission, providing a novel opportunity for an innovative therapy with transformative impact Day One's existing research and development expertise, and commercial capabilities, are well positioned to reach underserved patient populations, such as ACC Our Mission Inspired by the urgent needs of children, Day One creatively and intentionally develops new medicines for people of all ages with life - threatening diseases Emi - Le represents a potential first - in - class, targeted treatment option for patients with ACC Patients with Adenoid Cystic Carcinoma have no approved therapy

Transaction Rationale 7 Michael Vasconcelles Head of R&D

8 Emi - Le Represents A Transformational Opportunity To Address The Unmet Need For Patients With Adenoid Cystic Carcinoma (ACC) • ACC is a rare cancer, with an annual US incidence of ~1,300 patients 2 • Recurrent/metastatic ACC often presents with aggressive features; no approved therapeutic options exist 2 • B7 - H4