Day One Biopharmaceuticals : Corporate Presentation - April 2024

Day One Biopharmaceuticals

Targeted Therapies for People of All Ages

April 2024

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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 short-term investments to fund our operations, business plans and objectives, timing and success of our planned nonclinical and clinical development activities, the results of any of our strategic collaborations, including the potential achievement of milestones and provision of royalty payments thereunder, timing and results of nonclinical studies and clinical trials, efficacy and safety profiles of our products and product candidates, the ability of tovorafenib to treat pediatric low-grade glioma (pLGG) or related indications, the potential therapeutic benefits and economic value of our products and 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 inflation, changing interest rates, cybersecurity incidents, perceived instability in the global banking system, uncertainty with respect to the federal debt ceiling and budget and potential government shutdowns related thereto and global regional conflicts, 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 Annual Report on Form 10-K 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.

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Cancer Therapies for People of All Ages

Our Approach

• Develop medicines for genomically-defined cancers
• Establish first-in-class position through rapid registration pathways
• Expand to adolescent and adult populations in parallel and pursue those opportunities with the same commitment we do for children

3	Nasdaq: DAWN	IPO: 2021	Founded: 2018	Financial Position: Runway into 2026

Our Pipeline

Product Candidate	Therapeutic Area	Preclinical	Phase 1	Phase 2	Phase 3/	Approved	Recent & Anticipated
Registrational	Milestones

	BRAF-altered	FIREFLY-1 (pivotal Phase 2)	FDA approval:
Tovorafenib	Relapsed pLGG	April 2024
Type II RAF Inhibitor
OJEMDA brand name
in U.S.1	Frontline RAF-		First patient dosed:
	FIREFLY-2 (pivotal Phase 3)
	altered pLGG	March 2023

Pimasertib	MAPK-altered		Recommended Phase 2 dose &
solid tumors†	FIREFLIGHT-1† †	schedule expected:
MEK 1/2 Inhibitor
(Combo w/ tovorafenib)		2H 2024

VRK1 Program	Pediatric and	In-licensed§:
VRK1 Inhibitor	adult cancers	August 2023

• OJEMDA has received accelerated approval by the U.S. Food and Drug Administration. † Pimasertib Phase 1 dose escalation and expansion trial previously completed. † † Includes patients ≥12 years of age. §

• Research collaboration and license agreement with Sprint Bioscience AB for exclusive worldwide rights to a research-stage program targeting VRK1. pLGG, pediatric low-grade glioma. The safety and efficacy of investigational agents and/or investigational uses of approved products have not been established.

OJEMDATM (tovorafenib)

Relapsed or Refractory BRAF-altered pLGG

OJEMDA Now Approved In The U.S.

OJEMDA is the first and only FDA Approved therapy for the treatment of pediatric patients 6 months of age and older with relapsed or refractory pediatric low-gradeglioma harboring a BRAF fusion or rearrangement, or BRAF V600 mutation

• *This indication is approved under accelerated approval based on response rate and duration of response. Continued approval for this indication may be contingent upon verification of clinical benefit in a confirmatory trial.

pLGG Impact On Patients' Lives

Lily was diagnosed with an operable brain tumor at 5 months of age

7 Lily, lives with pLGG.

Pediatric Low-Grade Glioma: The Most Common Type Of Brain Tumor In Children

A Serious and Life-Threatening Disease

pLGGs are chronic and relentless, with patients suffering profound tumor and treatment-associated morbidity that can impact their life trajectory over the long term1

• For the majority of pLGG patients in the relapsed setting, there is no standard of care and no approved therapies
• Up to 75% of pLGGs have a BRAF alteration*, of those ~80% are BRAF fusions and ~20% are BRAF V600 mutations2-6
• Despite surgery playing a significant role in treatment, the vast majority of patients still require systemic therapy7,8
• Due to high rate of disease recurrence, most patients will undergo multiple lines of systemic therapy over the course of their disease

*Incidence of BRAF alterations varies across pLGG subtypes. 1 Sievert AJ, Fisher MJ. Pediatric low-grade gliomas. J Child Neurol. 2009;24(11):1397-1408. doi:10.1177/0883073809342005. 2 Penman CL et al. Front Oncol.

• 2015;5:54. 3 Cohen AR., N Engl J Med. 2020;386(20):1922-1931.4 Lassaletta A, et al. J Clin Oncol. 2017;35(25):2934-2941.5 Faulkner C, et al. J Neuropathol Exp Neurol. 2015;74(9):867-872.6 Packer RJ, et al. Neuro Oncol. 2017;19(6):750-761.7 Ostrum QT et al., Neuro Oncol. 2015; 16(Suppl 10):x1-x36;8 De Blank P. et al., Curr Opin Pediatr. 2019 Feb; 31(1):21-27.

Conventional Treatments Can Be Disruptive To Childhood And Can Have Significant Long-Term Consequences

Surgery

• Significant recovery times
• Risks of complications
• Resection may be limited by location of tumor
• Potential for functional deficits based on location of tumor and extent of resection

Chemotherapy

• Requirement for indwelling catheter and weekly infusions
• Risk of neutropenia, hypersensitivity reactions, nausea and vomiting and peripheral neuropathy

Radiation

• Risk of secondary malignancy
• Risk of malignant transformation
• Risk of vascular proliferation and stroke
• Neurocognitive impact, depending on location of tumor and radiation field

Goal of therapy is to control the tumor, minimize the burden of surgery, chemotherapy, and

radiation, and reduce the risk of life-long treatment and disease-related effects

	Source: 1. Heitzer AM, Raghubar K, Ris MD, et al. Neuropsychological functioning following surgery for pediatric low-grade glioma: a prospective longitudinal study. J Neurosurg Pediatr. 2019;1-9. doi:10.3171/2019.9.PEDS19357. 2. Bryant R. Managing side effects of childhood
9	cancer treatment. J Pediatr Nurs. 2003;18(2):113-125. doi:10.1053/jpdn.2003.11. 3. Zahnreich S, Schmidberger H. Childhood cancer: occurrence, treatment and risk of second primary malignancies. Cancers (Basel). 2021;13(11):2607. doi:10.3390/cancers/13112607. 4. National
Cancer Institute. Fertility issues in girls and women with cancer. http://www.cancer.gov. Accessed June 13, 2022. 5. Alessi I., Caroleo A.M., de Palma L., Mastronuzzi A., Pro S., Colafati G.S., Boni A., Della Vecchia N., Velardi M., Evangelisti M., et al. Short and Long-Term Toxicity
	in Pediatric Cancer Treatment: Central Nervous System Damage. Cancers. 2022;14:1540. doi: 10.3390/cancers14061540.

Overview U.S. Prescribing Information For OJEMDATM (tovorafenib)

Available in tablet formulation and pediatric-friendly powder

for oral suspension

INDICATION

OJEMDA is indicated for the treatment of pediatric patients 6 months of age and older with relapsed or refractory pediatric low-grade glioma harboring a BRAF fusion or rearrangement, or BRAF V600 mutation

RECOMMENDED DOSE

380 mg/m2 administered orally once weekly (not to exceed a dose of 600mg once weekly); OJEMDA can be taken with or without food

For full prescribing information, visit dayonebio.com

10 *This indication is approved under accelerated approval based on response rate and duration of response. Continued approval for this indication may be contingent upon verification of clinical benefit in a confirmatory trial.