CDKN2A and glioblastoma: Overall, despite high genetic and expression heterogeneity of GBM, the TCGA analysis indicates that three major signaling pathways associated with cell cycle, senescence, and apoptosis are commonly dysregulated: RTKs/Ras/PI3K (in 88% of GBM), MDM/P53/CDKN1A/CDKN2A/apoptosis (87%), and CDKN2A/CDKs/RB1 (78%) [6, 16].