EPAS1 and neoplasm: Cell response to hypoxia is mainly controlled by hypoxia-inducible factors (HIF), heterodimeric helix-loop-helix proteins composed of O2-labile alpha and constitutively expressed beta subunits (HIF1α, HIF2α, and HIF-1β), involved in coordinating the regulation of numerous mechanisms that enable tumor cells to adapt to the hostile environment [28].