HIF1A and neoplasm: As the primary cellular and systemic response to hypoxic stress, tumor cells in these regions induce the production of hypoxia-inducible factors (HIFs), master transcription regulators that consist of two subunits, the α subunit (HIF-1α, HIF-2α and HIF-3α) and the β subunit (HIF-1β) (Arnt) (1,2).