Phase IIA Study of Belzutifan in EPAS1-, EGLN1-, or VHL-Mutant Erythrocytosis

Some people develop erythrocytosis, a condition characterized by having too many red blood cells, because of inherited changes (mutations) in genes such as EPAS1, EGLN1, or VHL. These genes are involved in the body\'s oxygen-sensing pathway and can cause the body to produce excess red blood cells. High red blood cell counts can increase the risk of symptoms and complications, including headaches, blood clots, and cardiovascular problems. This study will evaluate whether belzutifan, a medication that blocks the activity of HIF-2α, can reduce red blood cell production and improve blood counts in patients with erythrocytosis caused by these genetic mutations. Participants will receive belzutifan and undergo regular clinical assessments and laboratory testing to monitor treatment response and safety. The results of this study may provide a new targeted treatment option for patients with hereditary erythrocytosis caused by abnormalities in the oxygen-sensing pathway.