MGMT and glioblastoma: Although DNA methylation of the MGMT gene promotor was shown to be a prognostic marker for treatment response of temozolomide in GBM [39], Brennan et al. reported that MGMT status distinguishes responders from non-responders to TMZ only among samples classified as classical subtype of GBM (n = 96), but not among other samples classified as proneural, mesenchymal, and neural subtypes of GBM (a total of n = 225) [40].