MGMT and glioblastoma: It is commonly believed that MGMT promoter methylation in patient tumors results in reduced MGMT protein production, and elimination of the DNA repair activity required for TMZ resistance as MGMT transcription may be repressed by promoter methylation in tumor cells (Brandes et al. 2017), according to Liu et al. (2006) and Pistollato et al. (2010), GBM stem cells, which the stem cell marker CD133 can recognize, express a high amount of MGMT and have significant tumor resistance to TMZ.