Day One Biopharmaceuticals : Corporate Presentation - January 2023

Day One Biopharmaceuticals

Targeted Therapies for People of All Ages

January 2023

Day One Biopharmaceuticals

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Disclaimer

This presentation and the accompanying oral commentary contain forward-looking statements that are based on our management's beliefs and assumptions and on information currently available to our management. Forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified. In some cases, you can identify forward-looking statements by terminology such as "may," "will," "should," "could," "expect," "plan," anticipate," "believe," "estimate," "predict," "intend," "potential," "would," "continue," "ongoing" or the negative of these terms or other comparable terminology. Forward-looking statements include all statements other than statements of historical fact contained in this presentation, including information concerning our future financial performance, including the sufficiency of our cash, cash equivalents and investments to fund our operations, business plans and objectives, timing and success of our planned nonclinical and clinical development activities, timing and results of nonclinical studies and clinical trials, efficacy and safety profiles of our product candidates, execution of the Phase 2 clinical trial for tovorafenib and the Phase 1b/2 clinical trial for tovorafenib and pimasertib as designed, any expectations about safety, efficacy, timing and ability to complete clinical trials and to obtain regulatory approvals for tovorafenib and other candidates in development, the ability of tovorafenib to treat pediatric low-grade glioma (pLGG) or related indications, the potential therapeutic benefits and economic value of our product candidates, potential growth opportunities, competitive position, industry environment and potential market opportunities, our ability to protect intellectual property and the impact of global business or macroeconomic conditions, including as a result of the COVID-19 pandemic, inflation and rising interest rates, on our business and operations.

Forward-looking statements are subject to known and unknown risks, uncertainties, assumptions and other factors. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. These factors, together with those that are described under the heading "Risk Factors" contained in our most recent Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission ("SEC") and other documents we file from time to time with the SEC, may cause our actual results, performance or achievements to differ materially and adversely from those anticipated or implied by our forward-looking statements.

In addition, statements that "we believe" and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this presentation, and although we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted a thorough inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

This presentation also contains estimates and other statistical data made by independent parties and by us relating to market size and growth and other data about our industry. This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions and estimates of our future performance and the future performance of the markets in which we operate are necessarily subject to a high degree of uncertainty and risk.

Day One Biopharmaceuticals

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Cancer Drug Development for People of All Ages

Mission That	Tovorafenib (DAY101)	Growing Portfolio and Runway
Creates Value	Lead Program	Beyond Clinical Milestones

• Day One's mission is to help children with cancer, from day one and every day after
• Develop medicines for genomically- defined cancers
• Establish first-in-class position through rapid pediatric registration
• Expand to adolescent and adult populations in parallel and pursue those opportunities with the same commitment we do for children

• Investigational, oral, CNS-penetrantpan-RAF inhibitor
• Being studied as tablets and pediatric-friendly liquid suspension
• Breakthrough Therapy Designation
• Rare Pediatric Disease Designation
• Orphan Drug Designation (US/EU)

• Two clinical-stage MEKi assets, in- licensed for combination trials
• Projected cash runway into 2025
• Upcoming key milestones
• • Planned NDA submission in 1H 2023
  • NDA data set will include additional follow up with data to be presented at a medical meeting in Q2 2023
  • First patient dosing in pivotal Phase 3 (FIREFLY-2 /LOGGIC), frontline trial expected Q1 2023

Day One Biopharmaceuticals

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A Senior Team with Deep Experience Developing and Commercializing Products in Pediatric and Adult Oncology Markets

Jeremy Bender, PhD, MBA		Samuel Blackman, MD, PhD		Charles York II, MBA
Chief Executive Officer		Chief Medical Officer & Founder		Chief Operating and Financial Officer
VP of Corporate Development at Gilead; COO Tizona		Pediatric Heme/Onc and Neuro-Onc; Oncology Clinical		CFO and Head of Corporate Development at Aeglea;
Therapeutics; CBO Sutro Biopharma; founding Board		Development at Mavupharma, Silverback, Juno, Seattle		Consulting CFO at Bridgepoint Consulting;
member of VaxCyte		Genetics, GSK		PricewaterhouseCoopers

Mike Preigh, PhD		Davy Chiodin, PharmD		Jaa Roberson		Adam Dubow
Chief Technical Officer		Chief Development Officer		Chief People Officer		General Counsel
Head of CMC at Array for 10+ years. Brought		VP Regulatory Science, Acerta/AZ; Global		Head of Human Resources at Bellicum		Chief Compliance & Ethics Officer at Bristol
>20 drug candidates to IND & clinical		Regulatory Leader, Pediatric Oncology,		Pharmaceuticals; Human Resources Roles at		Myers Squibb (BMS); Legal leadership roles at
development		Roche/Genentech		Achaogen, Roche/Genentech		BMS in the U.S., Asia and Europe; Partner at
						Sedgwick, Detert, Moran & Arnold

Day One Biopharmaceuticals

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Our Pipeline

						Recent &
Product Candidate	Indication	Preclinical	Phase 1	Phase 2	Phase 3	Anticipated
						Milestones

Tovorafenib (DAY101)

Type II Pan-RAF Inhibitor

• FDA Breakthrough Therapy Designation for relapsed pLGG
• FDA Rare Pediatric Disease Designation (PRV Eligible) for pLGG
• FDA Orphan Drug Designation for malignant glioma
• EC Orphan Designation for glioma

Relapsed pLGG FIREFLY-11 (pivotal)

Frontline pLGG FIREFLY-2 (pivotal)

RAF-altered	FIRELIGHT-1*
solid tumors2
(monotherapy)

Topline data presented:

January 2023

Pre-NDA meeting & NDA submission planned: 1H 2023

NDA data set presentation planned: Q2 2023

First patient dosing expected: Q1 2023

First patient dosed:

November 2021

Pimasertib	MAPK-altered	FIRELIGHT-1*
solid tumors3
MEK 1/2 Inhibitor
	(Combo w/tovorafenib)

First patient dosed: May 2022

*Includes patients ≥12 years of age. 1 FIREFLY-1 Arm 1 expected to support registration. 2 DAY101 adult monotherapy Phase 1 dose escalation and expansion trial previously completed. 3 Pimasertib Phase 1 dose escalation and
expansion trial previously completed. pLGG, pediatric low-grade glioma. Tovorafenib and Pimasertib are investigational products. Safety and efficacy have	not been established by any health authority.	5
Day One Biopharmaceuticals