IGF1 and glioblastoma: A variety of growth factors such as epidermal growth factor receptor (EGFR), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF, FGF-2), transforming growth factor (TGF)-α, and insulin-like growth factor (IGF)-1 are overexpressed in GBM and thus provide a growth advantage to neoplastic cells.