VEGFA and glioblastoma: In particular, the glioblastoma hypoxic microenvironment induces the expression of hypoxia-inducible factor (HIF) in both cell subpopulation, generating a downstream cascade of events that promotes the synthesis and the paracrine release of some factors, as vascular endothelial growth factor (VEGF) and angiopoietins, by GSCs towards GECs, allowing cell proliferation [30,31].