This is because there is substantial evidence that HIF-1 becomes active in perinecrotic regions after radiation treatment, inducing the expression of vascular endothelial cell growth factor, which potentially protects tumor blood vessels from the cytotoxic effects of radiation, assures the delivery of oxygen and nutrients to cancer cells, and eventually accelerates tumor growth after the radiation treatment [15,17–19,81]. Here, HIF1A is linked to cancer.