IGF1 and glioblastoma: In fact, several growth factor pathways that are aberrantly activated in glioblastomas, including platelet-derived growth factor (PDGF), insulin-like growth factor-1 (IGF-1), hepatocyte growth factor/scatter factor (HGF/SF), vascular endothelial growth factor (VEGF), and transforming growth factor-β (TGF-β) also converge to Ras activation.