Glioblastomas represent 40% of all tumors of the central nervous system (CNS) and are among the most lethal tumors. Temozolomide (TMZ) combined with radiotherapy was the first substance to significantly improve the overall survival (to 14.6 months) as compared to surgery and radiotherapy alone and increased the proportion of patients surviving more than 2 years to 26%. TMZ showed the best efficacy in patients with a methylated O6-methylguanine-DNA methyltransferase (MGMT) promoter in part by eliminating stem cell-like tumor cells. Among patients with a methylated MGMT promoter, the median survival after treatment with combined radio-chemotherapy was 21.7 months, as compared to 15.3 months among those who were assigned to radiotherapy only. In the absence of methylation of the MGMT promoter, there was a smaller and statistically insignificant difference in survival between the treatment groups.