MGMT and central nervous system cancer: 5 The activity of this repair enzyme correlates inversely with sensitivity to agents such as temozolomide, that form O6-alkylguanine DNA adducts.3,5,11 Expression of the MGMT gene is known to play a role in carcinogenesis as a number of malignancies, including gliomas, have increased MGMT expression due to lower levels of promoter methylation.2,5 When the MGMT promoter is unmethylated, the MGMT gene is expressed and, therefore, likely to be more effective in repairing DNA that has been damaged by alkylating chemotherapy,7,8,12 rendering treatment less effective.