EPAS1 and polycythemia: These phenotypes linked to HIF2α mutations have been collectively referred to as HIF2-driven disease, which has been broadly separated into two classes where Class 1 is causative of neuroendocrine tumors including paraganglioma, pheochromocytoma, and somatostatinoma (as well as possible hemangioma/hemangioblastoma) with or without polycythemia while Class 2 is causative of only polycythemia (Tarade et al., 2018).