Day One Appoints Charles N. York II as Chief Operating and Financial Officer and Expands Board of Directors with the Addition of Natalie Holles

Day One Biopharmaceuticals, a clinical-stage biopharmaceutical company focused on accelerating new, promising targeted therapies for children and adults with cancer, today announced the appointment of Charles N. York II as chief operating and financial officer and the addition of Natalie Holles to the Company's board of directors.

"Charles and Natalie are accomplished biopharmaceutical executives and bring significant financial, operational and corporate development expertise to Day One," said Jeremy Bender, Ph.D., chief executive officer of Day One. "This expansion of our management team and board comes at an exciting time for the Company and follows the recent completion of our Series B financing, as well as the initiation of the pivotal FIREFLY-1 study with DAY101 in pediatric low-grade glioma. Charles and Natalie's collective skill set will be an asset to Day One as we continue to diligently execute on our mission to advance important new cancer treatments for children and patients of all ages."

Charles N. York II as Chief Operating and Financial Officer

Mr. York joins Day One from Aeglea BioTherapeutics where he served as chief financial officer and head of corporate development and where he was a member of the leadership team since 2014. He brings more than 20 years of strategic capital formation and leadership experience to Day One. Prior to joining Aeglea, Mr. York served as consulting chief financial officer at Bridgepoint Consulting, focusing on growth stage life science companies. He earned his bachelor's degree in business administration and accounting from University of Connecticut and his MBA from the McCombs School of Business at The University of Texas at Austin.

"Day One represents one of the most exciting and focused new companies in the biopharmaceutical industry," said Mr. York. "I am thrilled to join this talented management team who shares an urgent sense to advance important new targeted cancer treatments for children and adults. I look forward to applying my experience and expertise as the Company enters the next phase of development, which begins with the DAY101 pivotal study as the anchor of our vision of new opportunities for the company and patients."

Natalie Holles to Board of Directors

Ms. Holles brings to Day One more than 20 years of experience in corporate development, strategic planning and commercial leadership. She currently serves as president and chief executive officer of Audentes Therapeutics, an Astellas company. Prior to joining Audentes, Ms. Holles served as senior vice president, corporate development at Hyperion Therapeutics (acquired by Horizon Pharma in 2015). Earlier, she served as vice president, business development at KAI Pharmaceuticals (acquired by Amgen in 2012) and held corporate development and commercial roles at InterMune (acquired by Roche in 2014) and Genentech. Ms. Holles holds an M.A. in molecular, cellular and developmental biology from the University of Colorado, Boulder, where she was a Howard Hughes Medical Institute predoctoral fellow, and an A.B. in human biology from Stanford University.

"Day One is making substantial progress, and I am excited to be part of this purpose-driven and execution-focused company," said Ms. Holles. "It is time for the industry to pursue the development of targeted cancer therapies for children with the same sense of urgency and speed as is typical for adult patient populations. Day One is a leader in this revolution."

About Day One Biopharmaceuticals

Day One Biopharmaceuticals is a differentiated company created to find and develop new therapies that meet the needs of people with cancer of all ages, starting with the biology of childhood cancer. The Company's name, Day One, was inspired by the "The Day One Talk"¹ that physicians have with patients and their families about an initial cancer diagnosis and treatment plan. Keeping the needs of patients and oncologists in mind, the Day One team focuses their efforts to bring medicines to families receiving this life-altering news. Together, we aim to re-envision cancer drug development and redefine what's possible for people with cancer ? whatever their age ? starting from Day One.

Day One partners with leading clinical oncologists, families, and scientists to identify, acquire, and develop important emerging cancer treatments. The Company's lead product candidate, DAY101, is designed as a first-in-class, oral, highly-selective pan-RAF kinase inhibitor, and the Company has initiated a Phase 2 registration-enabling study (FIREFLY-1) in pediatric, adolescent and young adult patients with recurrent or progressive low-grade glioma (pLGG). Based in South San Francisco, Day One has raised more than $190 million from leading life sciences investors. Through Day One and its collaborators, cancer drug development comes of age. For more information, please visit www.dayonebio.com.

¹Jennifer W. Mack and Holcombe E. Grier; Journal of Clinical Oncology 2004 22:3, 563-566