Growth factors, including tumor growth factor βeta (TGF-β), insulin-like growth factor (IGF), hepatoma-derived growth factor (HDGF), and glial cell-derived neurotrophic factor (GDNF), are upregulated in GBM and contribute to downstream Ras/Raf/MEK/ERK and PI3K/Akt signaling. This evidence concerns the gene GDNF and glioblastoma.