O6-methylguanine DNA methyltransferase (MGMT) is a well-known resistance factor that blunts the treatment effect of TMZ, by repairing the most toxic lesion.1,2 In almost 50% of patients with glioblastoma (GB) the MGMT gene promoter (MGMTp) is epigenetically silenced by methylation, while the second MGMT copy is usually lost in GB due to the recurrent loss of one copy of chromosome 10. The gene discussed is MGMT; the disease is glioblastoma.