HIF1A and paraganglioma: Interestingly, in a study of familial and sporadic pheochromocytomas and paragangliomas VEGF, hypoxia-inducible factor-1α and hypoxia-inducible factor-2 α (HIF-1α and HIF-2α) were prominently expressed in both tumor cells and in endothelial cells lining tumor blood vessels, and VEGF and HIF-1α and HIF-2α were more highly expressed in familial versus sporadic tumors.