VEGFA and glioblastoma: Through HIF-1 signalling, these hypoxic and necrotic niches activate and enrich glioblastoma stem cells (GSCs), induce the transdifferentation of GSCs into endothelial cells, and upregulate the release of pro-angiogenic growth factors, such as vascular endothelial growth factors (VEGF) and basic fibroblast growth factor (bFGF)4.