TGF-β induces expression of PDGF-A, which may serve as the primary mediator of TGF-β growth stimulatory effects.59 Instead of the standard Smad pathway that results in growth inhibition, TGF-β can deviate upstream of Smad to activate other mitogenic pathways implicated in GBM, including MAPK (Ras-Erk) and SAPK (Rho-JNK, TAK1-p38 kinase). The gene discussed is TGFB1; the disease is glioblastoma.