VHL and hemangioblastoma: Downregulation of HIF by VHL explains some of the phenotypes of tumors with VHL mutations: hemangioblastoma and clear cell renal carcinoma are highly vascular tumors, due at least in part to VEGF overproduction; hemangioblastoma, clear cell renal carcinoma and pheochromocytoma sometimes secrete erythropoietin, leading to overproduction of red blood cells.