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Inspired by the urgent needs of children, Day One creatively and
intentionally develops new medicines for people of all ages with life- threatening diseases 3
Bringing life-changing medicines to patients sooner Who we are
Commercial-stage biopharmaceutical company Our goal is to develop and provide access to targeted new medicines to patients of all ages as rapidly as possible Focused on advancing first- or best-in-class medicines for childhood and
adult diseases 2018 2021 2024 TM OJEMDA FOUNDED IPO APPROVAL Nasdaq: DAWN OJEMDA received approval in April 2024 and 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 4 fusion or rearrangement, or BRAF V600 mutation.
Positioned for accelerating growth in 2026 We build long-term value by
boldly advancing care for patients of all ages with high unmet needs 2026+ Growth Solidify OJEMDA as 2L SOC in r/r pLGG 2025 Execution 1L OJEMDA doubles pLGG 6 consecutive quarters of market opportunity double-digit growth
Global commercial Clinical execution of FIREFLY-2 expansion through Ipsen and DAY301 programs Data from DAY301 and 2024 Execution Acquisition of Mersana Therapeutics, including Emi-Le Emi-Le programs in ACC
Launched OJEMDA in the U.S. Emi-Le development with Strong balance sheet with path toward registration Acquisition of DAY301 1 ~$441M cash at year end 2025 (PTK7-Targeted ADC) 1 As used herein the term, "Cash" means
our cash, cash equivalents and short-term investments (unaudited) as of December 31, 2025. Cash, cash equivalents and short-term investments as of December 31, 2025 were 5 $441.1 million (unaudited). Standard of care in 2L relapsed or refractory
BRAF-altered pLGG. r/r, relapsed or refractory.
Our pipeline Phase 1 Phase 1 Product / Product Therapeutic Phase 3/
Recent & Anticipated Dose Dose Phase 2 Approved Candidate Area Registrational Milestones Escalation Expansion 1 3-year follow-up data publication OJEMDA submission (Tovorafenib) BRAF-altered Q1 2026 2 FIREFLY-1 (pivotal Phase 2) Type II RAF
Inhibitor relapsed pLGG CHMP positive opinion February 2026 Ex-U.S. Rights: Full enrollment 3 1H 2026 Front-line FIREFLY-2 (pivotal Phase 3) RAF-altered Topline data pLGG Mid-2027 to support potential 2028 approval Adenoid Emiltatug Cystic Phase 1
data Ledadotin (Emi-Le) Mid-2026 Carcinoma B7-H4-Targeted ADC (ACC) Adult and 4 DAY301 Phase 1a data pediatric solid 2H 2026 PTK7-Targeted ADC tumors 1 2 3 OJEMDA is brand name in U.S. and has received accelerated approval by the U.S. Food and Drug
Administration. FIREFLY-1 is an open-label, pivotal Phase 2 trial. Ex-U.S. license agreement with Ipsen to commercialize 4 OJEMDA (tovorafenib) outside the U.S. DAY301 is a license agreement with MabCare Therapeutics for exclusive worldwide rights,
excluding Greater China, for MTX-13/CB-002, a novel ADC targeting PTK7. The safety and efficacy of investigational agents and/or investigational uses of approved products have not been established. CHMP, Committee for Medicinal Products for Human
Well positioned for sustained growth and value generation OJEMDA
expansion Emi-Le OJEMDA $1B+ U.S. in R/R pLGG in 1L pLGG in ACC revenue opportunity in >$300M >$400M + >$500M + 3 high Durable, growing Expands earlier into Third, high-value unmet need revenue foundation treatment paradigm program
indications Additive topline revenue Near-term clinical catalysts 7
OJEMDA Relapsed or refractory BRAF-altered pLGG Nora Living with pLGG
Pediatric low-grade glioma: The most common type of brain tumor in
children A serious and life-threatening disease For the majority of patients with pLGG in the relapsed setting, there is no standard of care, and until recently, no approved therapies pLGGs are chronic and Up to 75% of pLGGs have a
BRAF alteration*, of those relentless, with patients ~80% are BRAF fusions and ~20% are BRAF V600 suffering profound tumor and 2-6 mutations treatment-associated morbidity that can impact their life Despite surgery playing a significant role
in treatment, 1 the vast majority of patients still require systemic trajectory over the long term 7,8 therapy Due to high rate of disease recurrence, most patients will undergo multiple lines of systemic therapy over the course of their
disease 1 2 *Incidence of BRAF alterations varies across pLGG subtypes. Sievert AJ, Fisher MJ. Pediatric low-grade gliomas. J Child Neurol. 2009;24(11):1397-1408. doi:10.1177/0883073809342005. Penman CL et al. Front Oncol. 3 4 5 6 2015;5:54. Cohen
AR., N Engl J Med. 2020;386(20):1922-1931. Lassaletta A, et al. J Clin Oncol. 2017;35(25):2934-2941. Faulkner C, et al. J Neuropathol Exp Neurol. 2015;74(9):867-872. Packer RJ, et al. Neuro 7 8 9 Oncol. 2017;19(6):750-761. Ostrum QT et al., Neuro
Oncol. 2015; 16(Suppl 10):x1-x36; De Blank P. et al., Curr Opin Pediatr. 2019 Feb; 31(1):21-27.
Overview U.S. prescribing information for OJEMDA 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 2 380 mg/m 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 * 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. 10 10
OJEMDA is redefining the treatment paradigm in relapsed or refractory
pLGG Clinical data reinforce OJEMDA's role in the r/r pLGG treatment paradigm Three-year follow-up data (Society for Neuro-Oncology 2025) reinforce durability of OJEMDA and align with how physicians manage pLGG Growing
long-term data and physician experience are driving OJEMDA toward standard of care in the evolving treatment paradigm for children with r/r pLGG 11
OJEMDA's durable clinical benefit supports its adoption as 2L SOC
1 OJEMDA Clinical Profile FIREFLY-1: 3-Year Data Median duration of response 19.4 months Durable responses, retreatment 1 feasibility Median time to next treatment 42.6 months Data consistent with chronic use in
77% of patients treatment-free at least 12 1 3,4 pediatric patients months following 24 months of therapy Minimal tumor rebound in first 6 months off Growing physician confidence, repeat 2 therapy utilization Early
OJEMDA retreatment experience: ~38% average tumor reduction (9 months median follow up, n=8) No new safety signals 1 2 3 FIREFLY-1 clinical trial data; long-term follow-up data presented at Society for Neuro-Oncology (SNO) 2025, Day One
Biopharmaceuticals clinical and commercial experience. 39 patients entered a treatment-free 12 4 observation period, Median treatment-free interval not yet reached.
Foundational U.S. opportunity for OJEMDA in both relapsed and frontline
pLGG Incident Therapeutic Build for New Illustrative pLGG Patient Flow Prevalence of Systemically-Treated Patients Under 25 Years ~26,000 pLGG Patients to be Treated in Frontline Setting Frontline (1L) Relapsed / Refractory (2L+) U.S.
Incident Patients <25 years old 1,2 ~5,500 with CNS Tumors (0.00521%) Annual Incident Patients Opportunity ~1,100 for OJEMDA in Rate of Low Grade Gliomas Treatment Eligible 2 ~2,600 Annual U.S. (Gliomas rate 63%, Low-Grade 77%) Population 1L
BRAF-Altered Treated r/r ~2,000-3,000 pLGG Patients pLGG 5 Year ~55-60% Eligible for Population in Prevalence Patients Ineligible for Surgery Systemic Therapy the U.S. ~1,500 2 ~5,500 or Post Surgery (58%) Progressed After Recurrences Trigger Rate
of BRAF-Altered 5 Years Entry to Treatment 3-7* ~1,100 (70%-75%) ~55-60% Eligible Population % BRAF Fusion (80%) % BRAF V600 (20%) ~880 ~220 Majority of patients with pLGG will progress within 5 years 1 2 3 4 5 US Census.
CBTRUS, Qaddoumi et al 2009, Schreck et al 2019, ClearView Analysis. Penman CL et al. Front Oncol. 2015;5:54. Cohen AR., N Engl J Med. 2020;386(20):1922-1931. Lassaletta A, et al. J Clin Oncol. 6 7 2017;35(25):2934-2941. Faulkner C, et al. J
Neuropathol Exp Neurol. 2015;74(9):867-872. Packer RJ, et al. Neuro Oncol. 2017;19(6):750-761. * Incidence of BRAF alterations varies across pLGG subtypes. Predominantly seen in pilocytic astrocytomas. May vary across pLGG
subtypes. BRAF, V-Raf murine sarcoma viral oncogene homolog B; MAPK, mitogen-activated protein kinase; pLGG, pediatric low-grade glioma. Estimated annual incidence, estimated prevalence, estimated progression rates, and estimated
recurrent/progressive total addressable opportunity are Day One calculations based on publicly available data. The estimated recurrent/progressive total addressable opportunity is based on progression free survival curves modeled from published
literature and internal market research conducted by EpidStrategies, A Division of ToxStrategies, Inc. on behalf of Day One. r/r, 13 13 relapsed or refractory.
OJEMDA has meaningful runway for increased utilization in the 2L+ pLGG
market Meaningful Runway for OJEMDA Increased Utilization ~1,100 unique r/r pLGG 2,3 Current penetration reflects only a treatment decisions annually portion of the addressable r/r market, indicating substantial headroom for OJEMDA share
growth 1 2 Treatment eligible population is calculated from epidemiology and progression curves; further validated by claims. Based on internal analysis of available U.S. claims data over a rolling 12-month period. Incidence verified by 3 14
independent third party, r/r pLGG patients with a treatment claim over a 12-month period.
Commercial execution and clinical impact driving strong revenue growth
OJEMDA Net Product Revenue OJEMDA Prescriptions (TRx) 1 1 $155.4M (+172%) in 2025 4,635 (+181%) in 2025 $52.8 1,394 2 2 (+37%) (+11%) 1,256 ~36% ~34% 1,062 CQGR CQGR $38.5 923 $33.6 $30.5 799 $29.0 610 $20.1 238 $8.2 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q2 Q3 Q4 Q1
Q2 Q3 Q4 Launch Launch 2024 2025 2024 2025 $Millions 2 Represents the comparison of full year 2024 (April 2024 approval) to full year 2025. Represents the comparison of 3Q 2025 to 4Q 2025. Prescriptions are approximations based on data
available as of December 31, 2025. 15
Commercial execution driving strong 2026 OJEMDA outlook OJEMDA U.S. Net
Product Revenue Named Patient Program Net Revenue Transitioned to Ipsen >50% growth at $225-$250M the midpoint FF-1 3-Year Follow-Up OJEMDA 2026 Expected Data Fuels Expected Net Product Revenue 2026 Growth: $155.4M Solidifying OJEMDA as
the 2L SOC Maximizing persistency to optimize patient outcomes 8 Months of Commercial Availability Continued highly favorable 1 $3.0M payer dynamics $54.2M 2024 2026 2025 Net Product Revenue 1 16 >50% growth represents the
comparison of 2025 to the midpoint of 2026 U.S. net product revenue guidance. 2024 net revenue included approximately $3.0M of revenue associated with Ex-U.S. sales.
Our strategy: focused execution to solidify OJEMDA as 2L standard of
care Drive New Patient Starts Increase depth of prescribing through continued evidence generation that reinforces how OJEMDA's clinical profile and benefits align with attributes physicians prioritize when treating pLGG patients* Optimize
Persistence Support physicians and patients to optimize their experience on OJEMDA including effective AE management and appropriate dose-adjustments * On label patients only. 17
Intellectual Property OJEMDA IP Composition of matter patent of
tovorafenib provides protection in summary and 1 the U.S. out to mid-2036 (with patent term extension) regulatory Patent portfolio covers formulations, manufacturing methods, and uses of tovorafenib, with issued and pending applications 2
designations potentially extending into the 2040s Regulatory Designations U.S. Orphan Drug Exclusivity (granted 7 years exclusivity) New Chemical Entity (granted 5 years exclusivity) Breakthrough Therapy Designation
Rare Pediatric Disease Designation Europe Orphan Drug Designation (eligible for 10 years exclusivity) 1 2 18 Composition of matter and pharmaceutical compositions of tovorafenib are co-owned; patent term extension is estimated at 5 years.
Future patent term coverage assumes pending applications are granted.
3-year follow- up data from the FIREFLY-1 trial studying OJEMDA Phase 2
After 26 OJEMDA cycles, patients could enter an observation period*
Updated 3-year analysis Time to next treatment, n=76 Subsequent anticancer therapy Treatment-free interval, n=39 or death Observation period OJEMDA Arm 1, n=77 Day 1 (no anticancer therapy) 26 cycles* (~24 months) Received 26 cycles,
n=44* PFS: RAPNO-LGG , n=76 PD or death Endpoints (Arm 1): Exploratory Primary ORR and CBR per RANO-LGG ORR per RANO-HGG Time to next treatment: composite endpoint of the time from the date of the first
OJEMDA dose to the start date of the Secondary first subsequent anticancer therapy (including retreatment with OJEMDA), or date of death, whichever was earlier Safety, ORR per RAPNO-LGG , Treatment-free interval:
composite endpoint of time from the last dose of OJEMDA to the start of subsequent treatment CBR, TTR, DOR, PFS based on or date of death, whichever was earlier RAPNO-LGG Post hoc Clinical progression: composite endpoint of
first visual PD, deteriorating clinical status, or death, whichever was earliest Radiographic progression: composite endpoint of first PD (>25% increase compared to nadir ) in target lesion and/or non-target lesion, any new