# EDGAR Filing Document

**Accession Number:** 0001845337
**File Stem:** 0001193125-26-084267
**Filing Date:** 2026-3
**Character Count:** 46852
**Document Hash:** 6754647bcda3e681a65550daf9046586
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-084267.hdr.sgml**: 20260302

**ACCESSION NUMBER**: 0001193125-26-084267

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 56

**CONFORMED PERIOD OF REPORT**: 20260302

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20260302

**DATE AS OF CHANGE**: 20260302

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Day One Biopharmaceuticals, Inc.
- **CENTRAL INDEX KEY:** 0001845337
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 832415215
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-40431
- **FILM NUMBER:** 26703532

**BUSINESS ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY, SUITE 200
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005
- **BUSINESS PHONE:** 650 484-0899

**MAIL ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY, SUITE 200
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Day One Biopharmaceuticals Holding Co LLC
- **DATE OF NAME CHANGE:** 20210209

?xml version='1.0' encoding='ASCII'? 8-K

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### WASHINGTON, D.C. 20549

### FORM 8-K

#### CURRENT REPORT

#### Pursuant to Section 13 or 15(d)

#### of the Securities Exchange Act of 1934

#### Date of Report (Date of earliest event reported): (March 2, 2026)

## DAY ONE BIOPHARMACEUTICALS, INC.

#### (Exact name of registrant as specified in its charter)

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| | | |
|:---|:---|:---|
| **Delaware** | **001-40431** | **83-2415215** |
| **(State or other jurisdiction**<br> **of incorporation)** | **(Commission**<br> **File Number)** | **(IRS Employer**<br> **Identification No.)** |

---

---

| | |
|:---|:---|
| **1800 Sierra Point Parkway, Suite 200** |  |
| **Brisbane, California** | **94005** |
| **(Address of principal executive offices)** | **(Zip Code)** |

---

#### Registrant's telephone number, including area code: (650) 484-0899

#### N/A

#### (Former name or former address, if changed since last report)
Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

---

| | | |
|:---|:---|:---|
| **Title of each class** | **Trading<br>Symbol(s)** | **Name of each exchange**<br> **on which registered** |
| Common Stock, par value $0.0001 per share | DAWN | Nasdaq Global Select Market |

---

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

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| | |
|:---|:---|
| **Item 7.01** | **Regulation FD Disclosure.**  |

---

On March 2, 2026, Day One Biopharmaceuticals, Inc. (the "Company") updated its corporate presentation to reflect that Ipsen Pharma SAS ("Ipsen") received a positive opinion from the Committee for Medicinal Products for Human Use of the European Medicines Agency recommending the conditional marketing authorization of OJEMDA<sup>TM</sup> (tovorafenib) as monotherapy for the treatment of children with relapsed or refractory BRAF-altered pediatric low-grade glioma. As previously announced, in July 2024, the Company entered into an exclusive license agreement with Ipsen to commercialize OJEMDA outside of the United States.

A copy of the updated corporate presentation is attached as Exhibit 99.1 to this Current Report on Form 8-K.

The information furnished in this Item 7.01, including Exhibit 99.1, shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference into any other filing under the Exchange Act or the Securities Act of 1933, as amended, except as expressly set forth by specific reference in such a filing.

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| | |
|:---|:---|
| **Item 9.01** | **Financial Statements and Exhibits.**  |

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(d) Exhibits

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| | |
|:---|:---|
| Exhibit<br>No. | Description |
| 99.1 | [Corporate Presentation](d104816dex991.htm) |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document) |

---

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#### SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

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| | | |
|:---|:---|:---|
|  | **DAY ONE BIOPHARMACEUTICALS, INC.** | **DAY ONE BIOPHARMACEUTICALS, INC.** |
| Date: March 2, 2026 | By: | /s/ Charles N. York II, M.B.A. |
|  |  | Charles N. York II, M.B.A. |
|  |  | Chief Operating Officer and Chief Financial Officer |

---

## Exhibit 99.1

![](g104816ex99_1p1g1.jpg)

Exhibit 99.1 Day One Biopharmaceuticals Targeted therapies for people of all ages March 2026

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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 commercialization and marketing efforts, timing and success of our planned nonclinical and clinical development activities, the potential benefits and therapeutic scope of our acquisitions and collaborations, including our acquisition of Mersana Therapeutics, Inc. and its lead product candidate, emiltatug ledadotin (XMT-1660), or Emi-Le, the results of any of our strategic collaborations, including the potential achievement of milestones and provision of royalty payments thereunder, efficacy and safety profiles of our products and product candidates, the ability of OJEMDA (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, fluctuating interest rates, supply chain disruptions, labor shortages or displacement, high unemployment rates, government shutdowns, significant political, trade or regulatory developments, including tariffs, shifting priorities within the U.S. Food and Drug Administration and reduced funding of federal healthcare programs, 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. 2

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![](g104816ex99_1p3g1.jpg)

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

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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.

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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 ü 6 consecutive quarters of market opportunity double-digit growth • Global commercial ü Clinical execution of FIREFLY-2 expansion through Ipsen and DAY301 programs • Data from DAY301 and 2024 Executionü Acquisition of Mersana Therapeutics, including Emi-Le Emi-Le programs in ACC ü Launched OJEMDA in the U.S. • Emi-Le development with ü Strong balance sheet with path toward registration ü 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.

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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 Use. 6

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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

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![](g104816ex99_1p8g1.jpg)

OJEMDA Relapsed or refractory BRAF-altered pLGG Nora Living with pLGG 8

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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.

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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

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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

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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.

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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.

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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.

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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 ¹ 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

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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.

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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

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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.

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3-year follow- up data from the FIREFLY-1 trial studying OJEMDA Phase 2 FIREFLY-1 Trial 19

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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 lesions, or death, whichever was earliest † June 6, 2025 data cutoff. \*A cycle was counted if a patient had at least 1 dose in a cycle; patients were treated for a planned period of 26 cycles, after which they could continue tovorafenib or opt to enter an observation period. 1 patient ‡ of 77 patients in Arm 1 had a target lesion not meeting the minimum size at baseline per IRC; the remaining 76 were included in the time to next treatment analysis. Among the 44 patients with ≥26 cycles, 9 did not enter post-treatment observation: 4 remain on primary treatment, 1 died, 2 discontinued due to PD, and 2 discontinued due to other reasons but opted out of post-treatment observation; among the 39 post-treatment observation patients, 4 received <26 ¥ ¶ cycles of treatment because of prolonged dose hold due to growth suppression. Hereafter referred to as RAPNO. Defined as the lowest tumor size (measured by SPPD per RAPNO) at any timepoint. CBR, clinical benefit rate; DOR, duration of response; HGG, high-grade glioma; IRC, independent radiology review committee; LGG, low-grade glioma; ORR, overall response rate; PFS, progression-free survival; RANO, Response Assessment in Neuro-Oncology; RAPNO, 20 Response Assessment in Pediatric Neuro-Oncology; PD, progressive disease; SPPD, sum of product of perpendicular diameters; TTR, time to response.

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Deep, durable responses with OJEMDA evaluated by IRC-assessed RAPNO Updated 3-year analysis 3-year Exposure \* Arm 1 (n=76) Completed ≥26 cycles of treatment, n (%) 44/76 (58) Response (IRC) † ORR, n (%) 40 (53) Best Overall Response, n (%) CR 0 PR 30 (39) MR 10 (13) ‡ SD 22 (29) PD 13 (17) NE 1 (1) ¥ Median change in tumor size, % (range) -47.3 (-97.3–162.0) ¶ Median DOR, months (95% CI) 19.4 (13.8–27.2) Median TTR, months (range) 5.4 (1.6–17.5) † June 6, 2025 data cutoff. \*1 patient of 77 had a target lesion not meeting the minimum size at baseline per IRC. ORR for RAPNO included MRs (i.e., ORR=CR+PR+MR). For CR, PR, and MR, confirmation of response by a subsequent ‡ ¥ ¶ scan approximately 3 months after the initial response was required. Of any duration. As measured by SPPD per RAPNO at last scan prior to last dose. Medians and 95% CIs were calculated using the Kaplan-Meier method; responders who had not progressed at the time of data cutoff were censored at the date of their last adequate imaging examination. CI, confidence interval; CR, complete response; DOR, duration of response; IRC, independent radiology review committee; MR, minor response; NE, not evaluable; ORR, overall response rate; PD, progressive disease; PR, partial response; RAPNO, Response Assessment in Pediatric Neuro-Oncology; SD, stable disease; 21 SPPD, sum of the products of the perpendicular diameters; TTR, time to response.

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Many patients continued OJEMDA beyond RAPNO-defined radiographic progression by IRC Updated 3-year analysis † In the 3-year follow-up analysis, 38 patients had RAPNO-defined PD while on OJEMDA 100% 75% OJEMDA ‡ Reduced tumor size 50% beyond PD: at last scan prior to 100% (38/38) last dose, relative to ≥26 cycles of baseline: Further tumor OJEMDA: 76% (29/38) 25% ‡ 66% (25/38) reduction beyond PD: 45% (17/38) 0% † June 6, 2025 data cutoff. \*1 patient of 77 had a target lesion not meeting the minimum size at baseline per IRC. 58 patients had RAPNO-defined PD events reported by the data cutoff. Of patients who had RAPNO-defined ‡ PD on tovorafenib, there are 37/38 patients with a scan at PD. One patient was assessed as having PD per RAPNO by IRC because of visual acuity. As measured by SPPD per RAPNO at EOT. EOT, end of treatment; IRC, 22 independent radiology review committee; PD, progressive disease; RAPNO, Response Assessment in Pediatric Neuro-Oncology; SPPD, sum of product of perpendicular diameters. Proportion of patients with PD while on tovorafenib (%)

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RAPNO PFS demonstrates efficacy with OJEMDA; time to next treatment more accurately reflects the full clinical benefit Updated 3-year analysis § Median time to next treatment was 42.6 months (95% CI 36.7–NE) • RAPNO defines radiographic PD 1.0 as a ≥25% increase in tumor size ₸ from nadir —not baseline 0.8 – Deep responses induced by Clinical PFS OJEMDA lower the PD threshold—modest 0.6 measurement variability on scans can score as PD † Time to next treatment 0.4 • Time to next treatment is a better assessment of clinical benefit than RAPNO PFS rPFS 0.2 – More closely aligned with PFS clinician-driven intervention than RAPNO PFS 0.0 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 Time from the first dose (months) † June 6, 2025 data cutoff. \*1 patient of 77 had a target lesion not meeting the minimum size at baseline per IRC. Time to next treatment: an exploratory composite endpoint of time from the date of the first tovorafenib dose ‡ to the start date of the first subsequent anticancer therapy (including retreatment with tovorafenib), or date of death, whichever was earlier. Clinical PFS = clinical deterioration per RAPNO, defined as neurologic or ¥ functional decline that is unequivocally attributable to tumor progression and not explained by treatment-related effects. RAPNO PFS event can occur due to either radiographic PD or clinical deterioration (clinical PD). ¶ § rPFS = radiographic progression per RAPNO, defined as a ≥25% increase in the tumor size (as measured by SPPD per RAPNO) of measurabl e lesions relative to the nadir, or the appearance of new lesions. Based on ₸ Kaplan-Meier estimate. Defined as the lowest tumor size (as measured by SPPD per RAPNO) at any timepoint. CI, confidence interval; IRC, independent radiology review committee; NE, not evaluable; NR, not reached; 23 PD, progressive disease; PFS, progression-free survival; RAPNO, Response Assessment in Pediatric Neuro-Oncology; rPFS, radiographic progression-free survival; SPPD, sum of product of perpendicular diameters. Probability

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Tumor rebound was minimal in the first 6 months off therapy Updated 3-year analysis 80 No tumor rebound (n=27) Tumor rebound (n=12)\* Post-treatment 60 observation patients, n=39 40 3 months 6 months † † post-EOT post-EOT 20 Median time between prior scan 1.8 (0–4.2) and last dose, months (range) 0 ‡ Median tumor size change from -51 -55 baseline (C1D1) after the last (-64, -33) (-67, -35) -20 dose, % (Q1, Q3) ‡ ≥25% increase in tumor size -40 from last scan prior to last dose, 12 (31%) n (%) -60 V600 mutation (n=6): -80 4 of 12 total patients with rebound 2 of 27 total patients without rebound -100 0 3 6 9 12 15 18 21 24 Last scan prior to last dose Months June 6, 2025 data cutoff. Time 0 is the date of the last tumor assessment before the final dose of primary tovorafenib treatment; plot lines extend to the last follow-up assessment (prior to tovorafenib retreatment if applicable). \*Tumor 1 † rebound was defined as a ≥25% increase in tumor size within 6 months of the last dose of tovorafenib as determined by the change in tumor size (as measured by SPPD per RAPNO) from the last scan before the final dose of tovorafenib. "3 ‡ months" is the first scan after the last dose, and "6 months" is any scan after EOT within 6 months. As measured by SPPD per RAPNO. C1D1, cycle 1, day 1; EOT, end of treatment (last dose); Q, quartile; RAPNO, Response Assessment in 24 Pediatric Neuro-Oncology; SPPD, sum of product of perpendicular diameters. Post-treatment observation period: Tumor kinetics after last scan prior to last dose (n=39). 1. O'Hare P, et al. Neuro Oncol. 2024;26(8):1357–1366. Change in tumor size (per RAPNO) compared with baseline (C1D1) during the observation period (%)

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Early evidence of retreatment activity observed in the OJEMDA-retreated cohort Updated 3-year analysis Patients retreated with OJEMDA n=8 At time of data cutoff: • All 8 patients receiving OJEMDA -38.3 Median change, % (range)\* (-80.9–0) retreatment were still on therapy † • Median tumor size was smaller 9.0 Median duration of retreatment, months (range) than the median tumor size (2.6–18.0) recorded prior to retreatment initiation Median number of tovorafenib cycles 10.5 administered during retreatment † June 6, 2025 data cutoff. \*Based on maximum % change from last scan before retreatment. As measured by SPPD per RAPNO. Post-treatment observation patients: OJEMDA retreatment (n=8). RAPNO, Response 25 Assessment in Pediatric Neuro-Oncology; SPPD, sum of product of perpendicular diameters.

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77% of 39 patients were treatment free for at least 12 months; median treatment-free interval not yet reached Updated 3-year analysis 100 90 Post-treatment observation † patients n=39 80 70 Median duration of treatment, months (range) 24.6 (16.0–38.7) 60 50 Treatment free Median follow-up from last dose to subsequent 40 16.0 (1.4–24.5) ≥12 months: anticancer therapy, months (range) 30 77% (30/39) 20 Treatment-free interval, months NR (NE–NE) Median (95% CI) 10 0 Post-treatment observation period † June 6, 2025 data cutoff. \*Treatment-free interval: an exploratory endpoint of time from the last dose of tovorafenib to the start of subsequent treatment or date of death, whichever was earlier. Among the 44 patients with ≥26 cycles, 9 did not enter post-treatment observation: 4 remain in primary treatment, 1 died, 2 discontinued due to PD and 2 discontinued due to other reasons but opted out of post-treatment observation; among the 39 post-treatment observation patients, 4 received <26 cycles of treatment because of prolonged dose hold due to growth suppression. Post-treatment observation period: Treatment-free interval (n=39). CI, confidence 26 interval; NE, not evaluable; NR, not reached; PD, progressive disease. Proportion of patients (%)

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No new safety signals were observed in the 3-year update Updated 3-year analysis Safety analysis set Safety analysis set Preferred term\* (n=137) (n=137), n (%) Grade ≥3 TRAEs, n (%) Any 91 (66) All TEAEs 137 (100) Decreased growth velocity 46 (34) All TRAEs 136 (99) Anemia 19 (14) Grade ≥3 TEAEs 113 (82) CPK increased 15 (11) Grade ≥3 TRAEs 91 (66) Maculopapular rash 11 (8) TEAEs leading to discontinuation 19 (14) ALT increased 7 (5) TRAEs leading to discontinuation 18 (13) June 6, 2025 data cutoff. Adverse events were cumulative events from day 1 to the earliest of (last dose + 30 days, start date of subsequent anticancer treatment, data cut, end of study). \*TRAEs reported at grade ≥3 in ≥5% of patients. AESI, adverse event of special interest; ALT, alanine aminotransferase; CPK, creatine phosphokinase; TEAEs, treatment-emergent adverse events; TRAEs, treatment-related adverse events. Safety analysis set (arms 27 1 & 2, n=137). 1. Kilburn LB, et al. Nat Med. 2024;30(1):207–217.

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FIREFLY-2 Pivotal Phase 3 trial of tovorafenib in front-line pLGG Bradon Living with pLGG since age 11 28

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FIREFLY-2: 1L pLGG approval represents the largest future growth lever for OJEMDA by doubling the commercial opportunity Estimated Annual 1 Treatment Decisions Key Value-Creation Milestones ~1,100 1L pLGG ~2,200 • FIREFLY-2 enrollment completion Total expected 1H 2026 Treatment • Topline data expected mid-2027, Decisions enabling potential 2028 approval ~1,100 Annually R/R pLGG Frontline expands OJEMDA's opportunity from a focused r/r market to the full treatment continuum 1 Based on internal analysis of available U.S. claims data over a rolling 12-month period. Incidence verified by independent third party. 29

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Expansion into front-line treatment represents a meaningful expansion opportunity for tovorafenib in pLGG Trial design Endpoints • Randomized, global, registrational Phase 3 trial of monotherapy tovorafenib • Primary endpoint: ORR based on RAPNO-LGG criteria, assessed by vs SoC chemotherapy blinded independent central review ‒ The ORR primary analysis is expected to occur ~12 months after the • Eligibility: Patients aged up to <25 years with LGG harboring a RAF alteration last patient randomized and requiring first-line systemic therapy • Key secondary endpoints: PFS and DoR by RAPNO-LGG criteria • Tovorafenib available as tablets and pediatric-friendly liquid suspension • Other secondary endpoints: changes in neurological and visual function, • Patients who progress after stopping tovorafenib may be re-challenged safety, and tolerability • Patients who progress in the SoC arm during or post-treatment may cross- • Key exploratory objectives: QoL and health utilization measures over to receive tovorafenib 2 Tovorafenib, 380mg/m QW Non-resectable or (not to exceed 600 mg) Stratified by sub-total resected LGG AND Long-term follow-up • Location of tumor Requiring first-line • Genomic alteration (48 months) systemic therapy Investigator's choice of • CDKN2A status vincristine/carboplatin\* or N ≈ 400 • Infant CHG diagnosis vinblastine or monthly carboplatin \* COG or SIOPe-LGG regimen. Abbreviations: CHG, chiasmatic, hypothalamic glioma; DoR, duration of response; LGG, low-grade glioma; ORR, objective response rate; QoL, quality of life; QW, once weekly; SoC, standard of care. 30 1:1 Randomization

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Emi-Le B7-H4-targeted antibody-drug conjugate (ADC) 31

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Emi-Le: Transformational opportunity in Adenoid Cystic Carcinoma (ACC) High-impact clinical program parallels ~3-year line of sight to OJEMDA's rapid development and potential approval and registration subsequent meaningful • Potential first-in-class program targeting a defined, treatment-resistant cancer commercial contribution, • High unmet medical need with limited with expected rapid therapeutic options • No approved treatments today adoption and time to peak • Potential rapid regulatory pathway 32

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Emi-Le Program Overview 1,2 Opportunity for Day One ACC patient population Emi-Le in ACC • Investigational B7-H4- • Annual U.S. incidence of • Emerging clinical data targeted ADC ~1,300 patients, conducive to rapid including: progression toward • Mechanism and registration modality well matched • ACC-1 subtype to ACC biology due to • Phase 1 data expected • Clinically aggressive highly and uniformly mid-2026 non-ACC-1 overexpressed B7-H4 • Potentially high-value, • Evidence of first-in-class growth monotherapy activity in opportunity aligned with ACC based on Phase 1 Day One's execution trial model 1 2 Adenoid Cystic Carcinoma Research Foundation, includes both frontline and relapsed ACC. 33

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DAY301 PTK7-targeted antibody-drug conjugate (ADC) 34

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DAY301: Next generation ADC targeting PTK7 Potential first-in-class asset Antibody DAY301 Structure • High-affinity PTK7-targeted IgG1 antibody optimized for tumor penetration while 1 limiting off-target exposure Payload • High-potency topo-1 payload with 2,3 enhanced bystander activity Polysarcosine sidechain (red arrow) PABC spacer (red scissor) Linker • Novel, hydrophilic, highly stable linker Upcoming Milestone platform enabling DAR 8 exatecan • Phase 1a data expected 2H 2026 delivery IP: Composition of Matter patent term expected 2044, once issued 1 2 3 Kong et al, Mol Cancer Ther. 2023;22(10):1128-1143, Joto et al, Int J Cancer 1997 72(4)680-6, Ogitani, Clin Can Res 201622 (20): 5097-5108. DAR, Drug to antibody ratio. 35

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PTK7: Well-suited as an ADC target Clinically validated ADC target PTK7 overview PTK7 is Broadly Expressed Across Structure: single-pass transmembrane Multiple Solid Tumor Types protein in the pseudokinase family of 1,2 receptor tyrosine kinases Expression: overexpressed in a broad range of solid tumors with low expression by IHC in most normal tissues, with moderate–high expression 3,4 in the female reproductive tract Function: catalytically inactive, but plays complex role in cancer cell biology and is involved in Wnt and VEGFR 3,5 signaling pathways Adapted from Kong et al, Mol Cancer Ther. 2023;22(10):1128-1143 Adapted from Mottard K, et al. Oncologist. 2024;oyae290. 1 2 3 4 Damelin M, et al. Sci Transl Med. 2017;9(372):eaag2611; Devang N, et al. Adv Protein Chem Struct Biol. 2021;124:121–185; Dessaux C, et al. Oncogene. 2024;43(26):1973–1984; https://www.proteinatlas.org/ Accessed May 2025; 5. Lhoumeau A-C, et al. Cell Cycle. 2011;10(8):1233–1236. ECD, extracellular domain; ICD, intracellular domain; Ig, immunoglobulin; IHC, immunohistochemistry; PTK7, protein tyrosine kinase 7; TM, 36 transmembrane; VEGFR, vascular endothelial growth factor receptor; Wnt, Wingless and Int-1.

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DAY301: Improved tumor regression activity demonstrated vs. benchmarks in multiple preclinical models PDX 362797 SCLC PDX 362310 TNBC PDX LD1-200615 HNSCC H-score 210 H-score 255 H-score 120 DAY301 has been designed to maximize therapeutic index to overcome limitations of prior PTK7 programs and standard chemotherapy Indicates drug administration Adapted from Kong C, et al. Mol Cancer Ther. 2023;22:1128–1143. 37

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DAY301: Initial Phase1a/b clinical trial design Phase 1a: Monotherapy Phase 1b: Monotherapy 1 Key Design Elements Dose Escalation Dose Expansion and Optimization • Simon 2-stage design, initial dose optimization • BOIN design for efficiency followed by expansion into RD1 and RD2 cohorts of dose escalation Dose Level 5 • Expand to registrational directed development • Backfill active dose levels after consultation with health authorities to generate additional safety data Dose Level 4 Recommended Simon 2-stage design • Enroll tumor types with Dose 1 Cohort known high PTK7 Recommended Dose Level 3 Dose 1 expression Recommended • Advance two Dose 2 Cohort Dose Level 2 recommended dose levels to Phase 1b Dose Level 1 • Pediatric dose confirmation Phase 1: Pediatric Monotherapy Dose Confirmation and efficacy assessment • Lower of the two adult recommended doses during Phase 1b Identify two recommended dose levels for further evaluation, based on safety and anti-tumor activity 1 Dose and schedule optimization are ongoing. The schematic above reflects the current planned dose-escalation and expansion framework and may be refined as clinical data mature.RD, Recommended Dose; BOIN, 38 Bayesian Optimal Interval.

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Summary 39

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Fourth quarter & full year 2025 financial results Three Months Ended Three Months Ended Full Year Ended Full Year Ended Financial Summary 12/31/25 12/31/24 12/31/25 12/31/24 ($ in millions) OJEMDA Net Revenue 52.8 29.0 155.4 57.2 License Revenue 0.9 0.2 2.8 73.9 Total Revenue $53.7 $29.2 $158.2 $131.2 Cost of Product and License Revenue 6.1 3.0 17.2 5.3 1 Research and Development Expense 40.9 61.8 148.1 227.7 2 Selling, General and Administrative Expense 34.2 29.8 120.6 115.5 Total Cost and Operating Expenses $81.2 $94.6 $285.9 $348.4 3 Non-operating Income 4.2 6.1 18.5 128.9 Income Tax Benefit (Expense) 2.0 (6.4) 2.0 (7.1) Net Income (Loss) ($21.3) ($65.7) ($107.3) ($95.5) 12/31/25 9/30/25 6/30/25 Cash, cash equivalents and short-term investments $441.1 $451.6 $453.1 1 All financial information is unaudited. Includes stock-based compensation expense of $3.4 million and $14.2 million for the three and twelve months ended 12/31/25, and $3.5 million and $16.7 million for the three 2 month and twelve months ended 12/31/24. Includes stock-based compensation expense of $7.7 million and $30.2 million for the three and twelve months ended 12/31/25, and $7.5 million and $31.6 million for the three 40 3 and twelve months ended 12/31/24. Includes sale of Priority Review Voucher of $108.0 million for the twelve months ended 12/31/24.

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Day One poised for a transformational 2026 Advancing Pipeline Deliver on 2026 net product revenue Advance Emi-Le: Deliver Phase 1 clinical guidance data by mid-2026, progress to later-stage development Complete FIREFLY-2 trial enrollment in 1H 2026, enabling mid-2027 data readout and Report Phase 1 updates from DAY301 and potential approval in 2028 inform next development steps Expand OJEMDA globally, extending commercial opportunity (Ipsen) 41

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Appendix 42

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Tovorafenib inhibits both BRAF fusions and BRAF V600 mutations MAPK RAS-independent activation of the Tovorafenib is an investigational, oral, pathway MAPK pathway selective, CNS-penetrant, type II RAF inhibitor that was designed to inhibit both monomeric and dimeric RAF kinase RAS • Activity in tumors driven by both RAF fusions and BRAF V600E mutations RAF RAF • Tablet and pediatric-friendly liquid RAF Tovorafenib suspension mutation fusion • Once weekly dosing Currently approved type I BRAF MEK inhibitors are indicated for use in patients with tumors bearing BRAF V600 mutations • Type I BRAF inhibitors cause ERK paradoxical MAPK activation in the setting of wild-type RAF, increasing the risk of tumor growth in BRAF fusion-driven Proliferation and survival Proliferation and survival Proliferation and survival Source: 1. Sun Y et al., Neuro Oncol. 2017; 19: 774–85; 2. Sievart AJ et al., PNAS. 2013; 110:5957-62; 3. Karajannis MA et al., Neuro Oncol 2014;16(10):1408-16. 43