GSTM1 and non-small cell lung carcinoma: It is the first to found GSTM1 null was associated with at least one methylation of p16, DAPK and RARβ gene promoters (OR = 1.67, 95% CI 1.01-2.77), supporting interaction between metabolic enzyme gene polymorphisms and hypermethylation of tumor suppressor genes in development of NSCLC [27,28].