Press Release

MUC16 is the highest-expressing ADC target in ovarian cancer, at least two-fold higher than other emerging targets

MUC16 is highly and stably expressed in the most aggressive and most common subtypes of endometrial cancer

Findings support Whitehawk's development of MUC16-directed ADC, HWK-016, currently being explored in Phase 1 for advanced ovarian and endometrial cancers

MORRISTOWN, N.J., April 10, 2026 /PRNewswire/ -- Whitehawk Therapeutics, Inc. (Nasdaq: WHWK), a clinical-stage oncology therapeutics company applying advanced technologies to established tumor biology to efficiently deliver improved antibody drug conjugate (ADC) cancer treatments, today presented three posters from a real-world analysis supporting the therapeutic potential of targeting mucin 16 (MUC16) with a next-generation ADC for the treatment of ovarian and endometrial cancers at the Society of Gynecologic Oncology (SGO) 2026 Annual Meeting on Women's Cancer, being held April 10-13, 2026, in San Juan, Puerto Rico. 

MUC16 is a cell-surface glycoprotein that promotes tumor cell proliferation, metastasis and immune evasion. MUC16 is overexpressed in multiple tumor types with limited expression in normal tissue. A large-scale RNA analysis demonstrated that MUC16 is highly and stably expressed across ovarian cancers and in the most aggressive and most common subtypes of endometrial cancer, including in later-stage disease, supporting its potential as a clinically meaningful ADC target and reinforcing the rationale for clinical development of HWK-016.

"Across both ovarian and endometrial cancers, MUC16 shows a high level of stable expression that is uncommon among many therapeutic targets," said Kathleen N. Moore, MD, Deputy Director and Director of Phase 1 Oncology Trials, The Fred & Pamela Buffett Cancer Center, University of Nebraska Medical Center. "The consistency of MUC16 expression across disease stage and platinum sensitivity supports the relevance of a MUC16-targeted ADC in earlier-line settings, as well as for heavily pretreated patients and as part of combination strategies."

Key Findings Include:

MUC16 in Ovarian Cancer

• MUC16 has high, tumor‑selective expression, with concordance between MUC16 mRNA expression and MUC16 protein abundance by IHC.
• MUC16 is highly expressed across most histologic subtypes, including the most common subtype, high-grade serous ovarian carcinoma (HGSOC), which accounts for ~70% of cases.
• In HGSOC, MUC16 expression is stable across disease stages, metastatic status and platinum sensitivity, underscoring relevance in early- and late-line treatment settings.
• MUC16 has the highest median expression, ranging from 2- to >100-fold higher than other clinically validated and emerging ADC targets, including NaPi2b, HER2, FRα, TROP2, B7-H4, CDH6 and CLDN6.

MUC16 in Endometrial Cancer

• MUC16 has high, tumor‑selective expression, with concordance with MUC16 protein abundance by IHC.
• MUC16 is most highly expressed in serous adenocarcinoma (the most aggressive subtype accounting for ~40% of deaths), followed by endometrioid adenocarcinoma (the most common subtype, accounting for ~90% of cases).
• In serous adenocarcinoma, MUC16 expression is stable across disease stages and metastatic status, and has the highest median expression, 1.4- to 3.7-fold higher than other clinically validated and emerging ADC targets, including NaPi2b, HER2, TROP2, FRα and B7H4.

Earlier MUC16‑directed ADCs targeted the cleaved extracellular portion of the protein (CA125), which is shed into circulation, limiting tumor delivery. HWK‑016, Whitehawk's investigational, next‑generation MUC16‑targeted ADC, is designed to overcome this antigen sink effect by selectively targeting the membrane‑bound, non‑shed portion of MUC16. HWK‑016 leverages a stable, cleavable linker to deliver a novel topoisomerase I (TOP1) inhibitor payload. HWK-016 is currently being evaluated in a Phase 1 clinical trial in patients with advanced ovarian and endometrial cancers [NCT07470853]. Initial clinical data are expected in the first half of 2027.

"The real-world data reported at SGO reinforce MUC16 as a 'super expressed' and durable target for gynecological cancers, strengthening the biological rationale for HWK-016," said Margaret Dugan, MD, Chief Medical Officer of Whitehawk Therapeutics. "By combining selective targeting of the membrane‑bound, non‑shed portion of MUC16 with our differentiated carbon‑bridge cystine‑repairing linker‑payload technology, HWK‑016 exemplifies our broader strategy of applying advanced ADC engineering to well‑validated tumor biology to potentially generate meaningfully improved outcomes for patients."

Poster Presentation Details:

Title: MUC16 in ovarian cancer: high, stable expression across histologic subtypes, disease stages, and platinum sensitivity status supports antibody-drug conjugate development
Presenter: Ursula A. Matulonis, MD, Dana-Farber Cancer Institute
Date & Time: April 12, 2026, 11:00 AM – 12:00 PM and 4:00 – 4:45 PM

Title: MUC16 as a therapeutic target: advancing antibody-drug conjugates for ovarian cancer treatment
Presenter: David M. O'Malley, MD, The Ohio State University
Date & Time: April 12, 2026, 11:00 AM – 12:00 PM and 4:00 – 4:45 PM

Title: High and stable MUC16 expression in endometrial cancer highlights potential for targeted antibody-drug conjugate development
Presenter: Kathleen N. Moore, MD, University of Nebraska Medical Center
Poster Tour – Group 9: Targeted Tactics and Therapies
Date & Time: April 12, 2026, 11:30 AM – 12:00 PM

The analysis was conducted as part of a previously announced collaboration between Whitehawk and Tempus AI. The posters will be accessible on the Presentations page of the Investors & News section of the Company's website at www.whitehawktx.com.

About Whitehawk Therapeutics 
Whitehawk Therapeutics is a clinical-stage oncology therapeutics company applying advanced technologies to established tumor biology to efficiently deliver improved cancer treatments. Whitehawk's advanced three-asset ADC portfolio is engineered to overcome the limitations of first-generation predecessors to deliver a meaningful impact for patients with difficult-to-treat cancers. These assets are in-licensed from WuXi Biologics under an exclusive development and global commercialization agreement. More information on the Company is available at www.whitehawktx.com and connect with us on LinkedIn.

Forward-Looking Statements
This press release contains certain forward-looking statements regarding the business of Whitehawk Therapeutics that are not a description of historical facts within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements are based on the Company's current beliefs and expectations and may include, but are not limited to, statements relating to expectations regarding the beneficial characteristics, optimized ADC design features, safety, efficacy, therapeutic effects, the size of the potential targeted markets with respect to HWK-016 and anticipated timing of the data release of initial Phase 1 data from clinical trial HWK-016 in the first half of 2027. Actual results could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation, uncertainties associated with clinical development of HWK-016, including potential delays in the commencement, enrollment and completion of clinical trials; failure to demonstrate the efficacy of clinical studies for HWK-016; and the risk that unforeseen adverse reactions or side effects may occur in the course of testing of HWK-016.

Additional risks and uncertainties that could cause actual outcomes and results to differ materially from those contemplated by the forward-looking statements are included in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2025, including under the caption "Item 1A. Risk Factors," and in Whitehawk's subsequent Quarterly Reports on Form 10-Q, and elsewhere in Whitehawk's reports and other documents that Whitehawk has filed, or will file, with the SEC from time to time and available at www.sec.gov.

All forward-looking statements in this press release are current only as of the date hereof and, except as required by applicable law, Whitehawk undertakes no obligation to revise or update any forward-looking statement, or to make any other forward-looking statements, whether as a result of new information, future events or otherwise. All forward-looking statements are qualified in their entirety by this cautionary statement. This cautionary statement is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.

Contact:

IR@whitehawktx.com

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SOURCE Whitehawk Therapeutics, Inc.