MGMT and cancer: Regulation of O6-MeG DNA methyltransferase (MGMT) (Hegi et al., 2005; Cancer Genome Atlas Research Network, 2008; Stupp et al., 2009; Jiang et al., 2014) and an absence of DNA mismatch repair (MMR) (Higuchi et al., 2020) are now widely recognized as the most important factors contributing to TMZ resistance in gliomas.