RB1 and glioblastoma: Three major altered pathways have been identified in GBM: (1) receptor tyrosine kinases including EGFR, PDGFR, cMET, PDGFR, Her2, and downstream ras and PI3K/PTEN/AKT/mTOR pathway (90%), (2) deregulations in TP53, MDM2, and MDM4 (around 85%), (3) Rb signaling and cell cycle-related pathways which include cyclins (3).