FDA Grants Priority Review to Merck’s Application for WELIREG® (belzutifan) for the Treatment of Patients With Advanced Pheochromocytoma and Paraganglioma (PPGL)

Rhea-AI Summary

Merck (MRK) announced the FDA's acceptance of a priority review for WELIREG® (belzutifan) to treat advanced pheochromocytoma and paraganglioma (PPGL) in adults and pediatric patients aged 12 and older. The application is based on data from the Phase 2 LITESPARK-015 trial, with a target action date of May 26, 2025.

If approved, WELIREG would become the only available therapy in the U.S. for eligible PPGL patients. The drug is already approved as the first and only HIF-2α inhibitor for treating von Hippel-Lindau (VHL) disease-associated tumors in the U.S., China, and 16 other countries. It's also approved in the U.S. and Canada for treating advanced renal cell carcinoma following specific prior treatments.

Positive

• First potential FDA-approved therapy for PPGL patients in the U.S.
• Priority review status granted by FDA
• Expanding indication potential for an already approved drug
• Global presence with approvals in multiple countries

Negative

• FDA decision not expected until May 2025
• Efficacy data from LITESPARK-015 trial not yet disclosed

Insights

Oncology Research Analyst

The FDA's priority review acceptance for WELIREG in advanced PPGL marks a strategic expansion of Merck's rare disease portfolio. PPGL represents a compelling market opportunity despite its rare status - orphan drugs typically command premium pricing and face competition due to high barriers to entry. This aligns with the industry trend toward rare disease therapeutics, which often generate substantial returns despite smaller patient populations.

WELIREG's potential approval would be particularly significant as it would be the first and only approved therapy for PPGL in the U.S. market. The drug's existing approvals in VHL disease and advanced RCC demonstrate its versatility across multiple rare oncologic indications. This strategic positioning allows Merck to leverage a single molecule across multiple high-value rare disease markets, maximizing the return on R&D investment.

The Phase 2 LITESPARK-015 trial data, while not yet publicly disclosed, must have shown compelling efficacy to warrant priority review. This accelerated pathway typically reduces the review period by 4 months, potentially giving Merck a significant first-mover advantage in the PPGL market. The expansion into pediatric patients (12 years and older) further broadens the addressable market.

This development strengthens Merck's position in the growing precision oncology space, particularly in HIF-2α inhibition. The company's broad clinical development program for WELIREG, including combination studies, suggests a long-term strategy to establish the drug as a cornerstone therapy across multiple rare oncologic indications.

Acceptance based on objective response rate data from the Phase 2 LITESPARK-015 trial evaluating WELIREG in certain patients with advanced PPGL

If approved, WELIREG would be the only available therapy in the U.S. for eligible patients with advanced PPGL

RAHWAY, N.J.--(BUSINESS WIRE)-- Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced the U.S. Food and Drug Administration (FDA) has accepted for priority review a supplemental new drug application (sNDA) seeking approval of WELIREG^® (belzutifan), Merck’s oral hypoxia-inducible factor-2 alpha (HIF-2α) inhibitor, for the treatment of adult and pediatric patients (12 years and older) with advanced, unresectable, or metastatic pheochromocytoma and paraganglioma (PPGL). The sNDA is based on objective response rate (ORR) and duration of response (DOR) data from the Phase 2 LITESPARK-015 trial, which will be presented at an upcoming medical meeting. The FDA has set a Prescription Drug User Fee Act (PDUFA), or target action, date of May 26, 2025.

“Pheochromocytoma and paraganglioma are rare tumors that form in and around the adrenal glands, and currently, there are no approved therapies available in the U.S. for patients with this rare disease,” said Dr. Marjorie Green, senior vice president and head of oncology, global clinical development, Merck Research Laboratories. “Today’s U.S. filing acceptance demonstrates our commitment to advancing novel therapies, such as WELIREG, to help treat patients with certain rare oncologic diseases. We look forward to working with the FDA to potentially provide this critical option to these patients who urgently need new innovative therapies.”

WELIREG is the first and only HIF-2α inhibitor therapy approved in the U.S. for the treatment of adult patients with von Hippel-Lindau (VHL) disease who require therapy for associated renal cell carcinoma (RCC), central nervous system hemangioblastomas, or pancreatic neuroendocrine tumors (pNETs) not requiring immediate surgery, based on results from the Phase 2 LITESPARK-004 trial. WELIREG is also approved for certain adult patients with VHL disease-associated tumors in China and 16 additional countries around the world.

WELIREG is also approved in the U.S. and Canada for the treatment of adult patients with advanced RCC following a PD-1/PD-L1 inhibitor and a vascular endothelial growth factor tyrosine kinase inhibitor (VEGF-TKI), based on results from the Phase 3 LITESPARK-005 trial.

Merck is investigating WELIREG in rare oncologic diseases, RCC and other tumor types through a broad clinical development program, including in Phase 2 and 3 trials evaluating WELIREG as monotherapy and in combination with other medicines.

About LITESPARK-015

LITESPARK-015 is an open-label, single-arm, multi-cohort Phase 2 trial (NCT04924075) evaluating the efficacy and safety of WELIREG monotherapy in patients with advanced PPGL (Cohort A1), pNETs (Cohort A2), VHL disease-associated tumors (Cohort B1), advanced gastrointestinal stromal tumors (Cohort C), or advanced solid tumors with HIF-2α-related genetic alterations (Cohort D). The primary endpoint is ORR per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) as assessed by blinded independent central review (BICR). Secondary endpoints include DOR, time to response, disease control, progression-free survival, overall survival and safety. The trial enrolled an estimated 322 patients who received WELIREG 120 mg orally once daily.

About pheochromocytoma and paraganglioma

Pheochromocytoma and paraganglioma (PPGL) are rare adrenal tumors that can be caused by certain genetic syndromes or mutations. It is estimated that up to 2,000 new cases of PPGL are diagnosed each year in the U.S., and up to 52,800 new cases are diagnosed each year worldwide. Pheochromocytoma occur in the center of the adrenal gland, whereas paraganglioma occur in nerve tissue in the adrenal glands and near certain blood vessels and nerves. Up to 25% of PPGL cases are metastatic at diagnosis.

About WELIREG^® (belzutifan) 40 mg tablets, for oral use

Indications in the U.S.

Certain von Hippel-Lindau (VHL) disease-associated tumors

WELIREG (belzutifan) is indicated for the treatment of adult patients with von Hippel-Lindau (VHL) disease who require therapy for associated renal cell carcinoma (RCC), central nervous system (CNS) hemangioblastomas, or pancreatic neuroendocrine tumors (pNET), not requiring immediate surgery.

Advanced Renal Cell Carcinoma (RCC)

WELIREG is indicated for the treatment of adult patients with advanced renal cell carcinoma (RCC) following a programmed death receptor-1 (PD-1) or programmed death ligand 1 (PD-L1) inhibitor and a vascular endothelial growth factor tyrosine kinase inhibitor (VEGF-TKI).

Selected Safety Information for WELIREG

Warning: Embryo-Fetal Toxicity

Exposure to WELIREG during pregnancy can cause embryo-fetal harm. Verify pregnancy status prior to the initiation of WELIREG. Advise patients of these risks and the need for effective non-hormonal contraception as WELIREG can render some hormonal contraceptives ineffective.

Anemia

WELIREG can cause severe anemia that can require blood transfusion. Monitor for anemia before initiation of, and periodically throughout, treatment. Transfuse patients as clinically indicated. For patients with hemoglobin <8 g/dL, withhold WELIREG until ≥8 g/dL, then resume at the same or reduced dose or permanently discontinue WELIREG, depending on the severity of anemia. For life-threatening anemia or when urgent intervention is indicated, withhold WELIREG until hemoglobin ≥8 g/dL, then resume at a reduced dose or permanently discontinue WELIREG.

In LITESPARK-004 (N=61), decreased hemoglobin occurred in 93% of patients with VHL disease and 7% had Grade 3 events. Median time to onset of anemia was 31 days (range: 1 day to 8.4 months).

The safety of erythropoiesis-stimulating agents (ESAs) for treatment of anemia in patients with VHL disease treated with WELIREG has not been established.

In LITESPARK-005 (n=372), decreased hemoglobin occurred in 88% of patients with advanced RCC and 29% had Grade 3 events. Median time to onset of anemia was 29 days (range: 1 day to 16.6 months). Of the patients with anemia, 22% received transfusions only, 20% received ESAs only, and 12% received both transfusion and ESAs.

Hypoxia

WELIREG can cause severe hypoxia that may require discontinuation, supplemental oxygen, or hospitalization.

Monitor oxygen saturation before initiation of, and periodically throughout, treatment. For decreased oxygen saturation with exercise (e.g., pulse oximeter <88% or PaO2 ≤55 mm Hg), consider withholding WELIREG until pulse oximetry with exercise is greater than 88%, then resume at the same or a reduced dose. For decreased oxygen saturation at rest (e.g., pulse oximeter <88% or PaO2 ≤55 mm Hg) or when urgent intervention is indicated, withhold WELIREG until resolved and resume at a reduced dose or discontinue. For life-threatening or recurrent symptomatic hypoxia, permanently discontinue WELIREG. Advise patients to report signs and symptoms of hypoxia immediately to a healthcare provider.

In LITESPARK-004, hypoxia occurred in 1.6% of patients.

In LITESPARK-005, hypoxia occurred in 15% of patients and 10% had Grade 3 events. Of the patients with hypoxia, 69% were treated with oxygen therapy. Median time to onset of hypoxia was 30.5 days (range: 1 day to 21.1 months).

Embryo-Fetal Toxicity

Based on findings in animals, WELIREG can cause fetal harm when administered to a pregnant woman.

Advise pregnant women and females of reproductive potential of the potential risk to the fetus. Advise females of reproductive potential to use effective non-hormonal contraception during treatment with WELIREG and for 1 week after the last dose. WELIREG can render some hormonal contraceptives ineffective. Advise male patients with female partners of reproductive potential to use effective contraception during treatment with WELIREG and for 1 week after the last dose.

Adverse Reactions

In LITESPARK-004, serious adverse reactions occurred in 15% of patients, including anemia, hypoxia, anaphylaxis reaction, retinal detachment, and central retinal vein occlusion (1 patient each).

WELIREG was permanently discontinued due to adverse reactions in 3.3% of patients for dizziness and opioid overdose (1.6% each).

Dosage interruptions due to an adverse reaction occurred in 39% of patients. Those which required dosage interruption in >2% of patients were fatigue, decreased hemoglobin, anemia, nausea, abdominal pain, headache, and influenza-like illness.

Dose reductions due to an adverse reaction occurred in 13% of patients. The most frequently reported adverse reaction which required dose reduction was fatigue (7%).

The most common adverse reactions (≥25%), including laboratory abnormalities, that occurred in patients who received WELIREG were decreased hemoglobin (93%), fatigue (64%), increased creatinine (64%), headache (39%), dizziness (38%), increased glucose (34%), and nausea (31%).

In LITESPARK-005, serious adverse reactions occurred in 38% of patients. The most frequently reported serious adverse reactions were hypoxia (7%), anemia (5%), pneumonia (3.5%), hemorrhage (3%), and pleural effusion (2.2%). Fatal adverse reactions occurred in 3.2% of patients who received WELIREG, including sepsis (0.5%) and hemorrhage (0.5%).

WELIREG was permanently discontinued due to adverse reactions in 6% of patients. Adverse reactions which resulted in permanent discontinuation (≥0.5%) were hypoxia (1.1%) and hemorrhage (0.5%).

Dosage interruptions due to an adverse reaction occurred in 39% of patients. Of the patients who received WELIREG, 28% were 65 to 74 years, and 10% were 75 years and over. Dose interruptions occurred in 48% of patients ≥65 years of age and in 34% of younger patients. Adverse reactions which required dosage interruption in ≥2% of patients were anemia (8%), hypoxia (5%), COVID-19 (4.3%), fatigue (3.2%), and hemorrhage (2.2%).

Dose reductions due to an adverse reaction occurred in 13% of patients. Dose reductions occurred in 18% of patients ≥65 years of age and in 10% of younger patients. The most frequently reported adverse reactions which required dose reduction (≥1.0%) were hypoxia (5%) and anemia (3.2%).

The most common (≥25%) adverse reactions, including laboratory abnormalities, were decreased hemoglobin (88%), fatigue (43%), musculoskeletal pain (33%), increased creatinine (34%), decreased lymphocytes (34%), increased alanine aminotransferase (32%), decreased sodium (31%), increased potassium (29%), and increased aspartate aminotransferase (27%).

Drug Interactions

Coadministration of WELIREG with inhibitors of UGT2B17 or CYP2C19 increases plasma exposure of belzutifan, which may increase the incidence and severity of adverse reactions. Monitor for anemia and hypoxia and reduce the dosage of WELIREG as recommended.

Coadministration of WELIREG with CYP3A4 substrates decreases concentrations of CYP3A4 substrates, which may reduce the efficacy of these substrates or lead to therapeutic failures. Avoid coadministration with sensitive CYP3A4 substrates. If coadministration cannot be avoided, increase the sensitive CYP3A4 substrate dosage in accordance with its Prescribing Information. Coadministration of WELIREG with hormonal contraceptives may lead to contraceptive failure or an increase in breakthrough bleeding.

Lactation

Because of the potential for serious adverse reactions in breastfed children, advise women not to breastfeed during treatment with WELIREG and for 1 week after the last dose.

Females and Males of Reproductive Potential

WELIREG can cause fetal harm when administered to a pregnant woman. Verify the pregnancy status of females of reproductive potential prior to initiating treatment with WELIREG.

Use of WELIREG may reduce the efficacy of hormonal contraceptives. Advise females of reproductive potential to use effective non-hormonal contraception during treatment with WELIREG and for 1 week after the last dose. Advise males with female partners of reproductive potential to use effective contraception during treatment with WELIREG and for 1 week after the last dose.

Based on findings in animals, WELIREG may impair fertility in males and females of reproductive potential and the reversibility of this effect is unknown.

Pediatric Use

Safety and effectiveness of WELIREG in pediatric patients under 18 years of age have not been established.

Merck’s focus on cancer

Every day, we follow the science as we work to discover innovations that can help patients, no matter what stage of cancer they have. As a leading oncology company, we are pursuing research where scientific opportunity and medical need converge, underpinned by our diverse pipeline of more than 25 novel mechanisms. With one of the largest clinical development programs across more than 30 tumor types, we strive to advance breakthrough science that will shape the future of oncology. By addressing barriers to clinical trial participation, screening and treatment, we work with urgency to reduce disparities and help ensure patients have access to high-quality cancer care. Our unwavering commitment is what will bring us closer to our goal of bringing life to more patients with cancer. For more information, visit https://www.merck.com/research/oncology.

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

Forward-Looking Statement of Merck & Co., Inc., Rahway, N.J., USA

This news release of Merck & Co., Inc., Rahway, N.J., USA (the “company”) includes “forward-looking statements” within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. There can be no guarantees with respect to pipeline candidates that the candidates will receive the necessary regulatory approvals or that they will prove to be commercially successful. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of pharmaceutical industry regulation and health care legislation in the United States and internationally; global trends toward health care cost containment; technological advances, new products and patents attained by competitors; challenges inherent in new product development, including obtaining regulatory approval; the company’s ability to accurately predict future market conditions; manufacturing difficulties or delays; financial instability of international economies and sovereign risk; dependence on the effectiveness of the company’s patents and other protections for innovation products; and the exposure to litigation, including patent litigation, and/or regulatory actions.

The company undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in the company’s Annual Report on Form 10-K for the year ended December 31, 2023 and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (www.sec.gov).

Please see Prescribing Information, including information for the Boxed Warning about embryo-fetal toxicity, for WELIREG (belzutifan) at https://www.merck.com/product/usa/pi_circulars/w/welireg/welireg_pi.pdf and Medication Guide for WELIREG at https://www.merck.com/product/usa/pi_circulars/w/welireg/welireg_mg.pdf. 

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Source: Merck & Co., Inc.

FAQ

When is the FDA PDUFA date for Merck's (MRK) WELIREG PPGL treatment application?

The FDA has set a PDUFA date of May 26, 2025, for Merck's supplemental new drug application for WELIREG in PPGL treatment.

What patient population would Merck's (MRK) WELIREG treat for PPGL?

WELIREG would treat adult and pediatric patients (12 years and older) with advanced, unresectable, or metastatic pheochromocytoma and paraganglioma (PPGL).

What clinical trial supports Merck's (MRK) WELIREG application for PPGL?

The application is supported by objective response rate and duration of response data from the Phase 2 LITESPARK-015 trial.

What other indications is Merck's (MRK) WELIREG currently approved for?

WELIREG is approved for von Hippel-Lindau (VHL) disease-associated tumors and advanced renal cell carcinoma following specific prior treatments.

How would Merck's (MRK) WELIREG position in the PPGL market if approved?

If approved, WELIREG would be the only available therapy in the U.S. for eligible patients with advanced PPGL.