We have chosen the breast cancer cell line MCF-7 as a system because we have already shown that the HIF-1α and HIF-2α proteins are present and stabilized across different hypoxia time points, starting at 16 h, and we have characterised the role of both HIF-1α and HIF-2α in the regulation of gene expression in this system [25,26]. The gene discussed is HIF1A; the disease is breast cancer.