Peloton was one of a handful of cancer-focused biotech companies acquired since 2018 by Merck, which has sought to complement its top-selling immunotherapy Keytruda with a broad pipeline in oncology. During that stretch, Merck has spent some $7 billion on deals for Viralytics, Immune Design, Peloton, ArQule and VelosBio.

Welireg is the first drug from that group to win FDA approval, becoming the first systemic treatment for cancers linked to VHL, a disease estimated to affect about 10,000 Americans.

People with VHL can develop benign tumors in their blood vessels, as well as ones that are cancerous. For its study of Welireg, Merck enrolled people with VHL-associated kidney cancer, some of whom also had tumors in their central nervous and neuroendocrine systems.

In about half of the 61 study participants, treatment shrank the tumors located in their kidneys, although not completely. The drug was also effective against tumors that had emerged elsewhere, with slightly higher rates of response to treatment.

Welireg is associated with significant side effects, however, including a serious risk of embryo-fetal harm that led the FDA to place a black box warning on the drug’s label. Treatment can also make ineffective hormonal contraceptives and lead to severe anemia and hypoxia.

In testing, side effects led to permanent discontinuation of treatment in two study participants and to dose interruptions in 24.

Merck priced Welireg at a wholesale cost of $26,400 per month, according to a company spokesperson. Supplies of the drug will be available commercially in early September, the spokesperson said.

While Welireg is the first HIF-2 alpha inhibitor approved by the FDA, there are several others in development. Arrowhead Pharmaceuticals is testing one in a Phase 1 trial, while Arcus Biosciences expects to begin human study of another later this year.