MGMT and glioblastoma: O6-alkylguanine DNA alkyltransferase (MGMT), which provides the main line of defense against DNA alkylating agents such as TMZ, has been found to be epigenetically silenced through DNA methylation in a large fraction of glioblastoma tumors (Karayan-Tapon et al., 2010; Hegi et al., 2005).