TP53 and glioblastoma: Moreover, hypermethylation of the CpG island in promoters of genes involved in signalling pathways often deregulated in these tumours have been reported, with RB1 methylation observed in 14% of glioblastomas analysed (5 of 35), PTEN promoter methylation in 35% (27 of 77) glioblastoma patients' samples, and TP53 promoter methylation in 21.4% (9 of 42) glioblastoma [35, 36, 37, 38, 39, 40].