Deficiency in the expression of MGMT (O-6-Methylguanine-DNA Methyltransferase) either through low protein expression and/or silencing of the MGMT promoter, along with a functional DNA mismatch repair (MMR) pathway, is associated with temozolomide activity in several cancer types; in patients with glioblastoma, MGMT promoter methylation status is predictive of response to the drug (3–7). The gene discussed is MGMT; the disease is glioblastoma.