RB1 and glioblastoma: The most common mutations influence PI3K/AKT/mTOR, Ras/RAF/MAPK, and p53/Rb signalling pathways.58–61 These include mutations in TP53, PTEN, and CDK4. 62–68 TP53 signalling is altered in 87% of glioblastomas, mostly affecting p53, murine double minute-2 (MDM2), MDM4, and cyclin-dependent kinase (CDK) N2A genes.