RB1 and glioblastoma: Despite this heterogeneity, a large-scale analysis of genetic aberrations in GBM identified three main signalling pathways that are commonly dysregulated: activation of the receptor tyrosine kinase (RTK)/Ras/phosphoinositide 3-kinase (PI3K) pathway (88%), inhibition of p53 (87%), and retinoblastoma protein (Rb) signalling pathways (78%) (34).