Although methylation at the cytosine of CpG regions is common [69], methylation of guanine at the N-7 and O-6 positions of guanine, referred to as N7MeG (or 7-MG) and O6MeG, respectively, that are controlled by mettl1 (Methyltransferase 1, tRNA methyl-guanosine) and mgmt (O6-methylguanine-DNA methyltransferase), respectively, have also been described, especially for cancers and cell viability [70,71]. This evidence concerns the gene MGMT and cancer.