HQ Team
May 15, 2025: Merck & Co. got approval from the US Food and Drug Administration for a pill to treat a rare type of tumour in adults and children aged above 12 years, according to a statement.
Merck’s medicine, Welireg (belzutifan), treats a rare type of tumour called pheochromocytoma or paraganglioma (PPGL), according to a Merck statement.
These tumours come from the same body tissue but grow in different places — pheochromocytomas grow in the adrenal glands (which sit on top of the kidneys), and paragangliomas grow outside the adrenal glands.
About 52,800 new PPGL cases are diagnosed each year worldwide. Sometimes, these tumours happen because of inherited genetic problems and cannot be removed by surgery.
Shrink or control
The FDA’s approval is based on results from a clinical study, which showed that this medicine helped shrink or control these tumours in patients.
The study enrolled 72 patients in a single cohort who had measurable disease verified by blinded independent central review and documented histopathological diagnosis of PPGL.
The patients also had locally advanced or metastatic disease that was not amenable to surgery or curative treatment, and adequately controlled blood pressure. Patients received the pill at a dose of 120 mg once daily until disease progression or unacceptable toxicity.
The major measure used to see how well the treatment works for advanced PPGL was the Objective Response Rate (ORR). This was assessed by experts who reviewed scans without knowing patient details (called Blinded Independent Central Review or BICR) using a standard method called RECIST version 1.1, which checks how much the tumours shrink or disappear.
Show improvement
Other important measures included the Duration of Response, or how long the tumour stays smaller or controlled after treatment starts and Time to Response or how quickly patients begin to show improvement after starting treatment.
The ORR was 26% — about one in four patients had their tumours shrink significantly. The median duration of response was over 20 months, showing that the effect lasted a long time for many patients.
Some patients were also able to reduce their blood pressure medicines by half or more for at least six months, which is important because these tumours often cause high blood pressure.
“PPGL, sometimes referred to as pheo para, is a rare condition affecting up to 2,000 people each year in the United States,” said Dr Camilo Jimenez, professor, Department of Endocrine Neoplasia and Hormonal Disorders at the University of Texas MD Anderson Cancer Center.
“Patients with these tumours, which arise from the adrenal glands and the extra-adrenal paraganglia, may require specialised care due to their complexity and rare nature, often posing significant challenges for both diagnosis and treatment,” he said.
Boxed warning
Dr Marjorie Green, senior vice president and head of oncology, global clinical development, Merck Research Laboratories, said: “For patients with advanced PPGL, there has been a lack of approved systemic treatment options available to help manage their disease, underscoring the importance of this approval in the US.”
“This approval marks the third indication for Welireg in the US and demonstrates our company’s commitment to providing innovative cancer therapies for patients in need, including those with rare diseases,” she said.
The pill comes with a boxed warning.
Exposure to the pill during pregnancy can cause embryo-fetal harm. It can render some hormonal contraceptives ineffective and can cause severe anaemia that can require a blood transfusion.
Monitoring is required for anaemia before initiation of and periodically throughout treatment. The pill can cause severe hypoxia that may require discontinuation, supplemental oxygen, or hospitalisation.
