In MCF-7 human breast cancer cells, both HIF-1α and HIF-2α primarily bind relatively GC rich DNAse1 sensitive genomic regions, reflecting the concentration of hypoxia response elements (HRE) within chromatin accessible promoter regions and over 500 such HIF-binding sites have been identified across the human genome [92, 103]. This evidence concerns the gene EPAS1 and breast carcinoma.