HIF1A and neoplasm: VEGF, also activated by hypoxia-inducible factor-1a (HIF-1a) and released by tumor cells, dominates this extremely complex mechanism, while other proangiogenic features include angiopoietin-2, fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), transforming growth factor-β (TGF-β), and interleukin-8 (IL-8) [54].