Prognosis and response to therapy are known to be better in patients with a methylated MGMT promoter gene. Epigenetic silencing of MGMT by promoter methylation is an important factor in predicting outcome for patients with GBM treated with temozolomide. Approximately 66% of GBM tumors are MGMT unmethylated (high expression of MGMT), which through a MGMT repair mechanism, confers resistance to temozolomide, the standard chemotherapy treatment of GBM.