MGMT and glioblastoma: The clinical presentation and response to treatment can be variable between GBM patients, in part owing to a strong inter-tumoural heterogeneity as evidenced by the occurrence of different gene mutations affecting defined signalling networks [6, 11], the identification of several molecular subtypes [44, 55] including a Glioma CpG Island Methylator phenotype (G-CIMP) [40] and the variability in the methylation pattern of the O-6-methylguanine-DNA methyltransferase (MGMT) gene.