MGMT and cancer: O6-methyguanine DNA methyltransferase (MGMT), a DNA repair protein encoded by MGMT gene that located at 10q26, removed cytotoxic and mutagenic adducts from the O6-guanine of DNA.[11] Alkylation at the O6 position of guanine in DNA contributed a lot to the emergence of gene variation in cancers, because thymine tended to replace cytosine to pair with O6-methylguanine in the replication of DNA, which eventually resulted in the G > A mutation.