It involves the secretion of pro-angiogenic factors such as angiopoietin (Ang)-1, which, in concert with vascular endothelial growth factor (VEGF)-A, has been shown to induce angiogenesis in xenograft models [69], and Ang-2, which can mediate tumor angiogenesis in astrocytomas [70]. This evidence concerns the gene VEGFA and astrocytoma (excluding glioblastoma).