ARNT and neoplasm: HIF exists as three isoforms (1–3), with HIF-1 and, to a lesser extent, HIF-2 identified as drivers of tumour growth.[2] HIF-1 is a heterodimer made up of two subunits: HIF-1α and HIF-1β (HIF-1β is also referred to as aryl hydrocarbon receptor nuclear translocator, ARNT).