The first group has both HIF-1α and HIF-2α expressed to drive tumour progression, whereas in the second group, the effect of only HIF-2α prevails, particularly in vivo in rapidly proliferating tumours where access to nutrients is limited for tumour cells, resulting in enhanced tumour cell proliferation/angiogenesis and poor patient prognosis [16]. This evidence concerns the gene HIF1A and neoplasm.