MGMT and glioblastoma: The low efficiency of RT/TMZ and adjuvant TMZ may nevertheless be due to the fact that (a) not all tumor cells proliferate with the resting fraction to be therapy-refractory, (b) MGMT is expressed but below the detection level, (c) MMR is down- and HR up-regulated, (d) glioblastoma cells inefficiently complete apoptosis, and (e) the majority of proliferating tumor fraction goes into therapy-induced senescence.