MGMT and glioblastoma: On the other hand, GBM tumors with high levels of MGMT and, consequently, increased DNA repair, commonly display TMZ resistance, and a strong TMZ chemo-resistant phenotype can be acquired with decreased MGMT promoter methylation over the course of tumor treatment, progression and recurrence; thus, the MGMT promoter methylation status is a crucial indicator of the patients’ outcome [3].