MGMT and central nervous system cancer: Although the MGMT enzyme is known as an unpleasant protein that reverses and neutralizes the cytotoxic effect of TMZ, epigenetic evidences show that CpG island promoter hypermethylation of the MGMT promoter actually occurs in some glioma cells, then regulates the expression of MGMT genes, which prevents the synthesis of MGMT enzyme [16,17,18].