GSTM1 and lung cancer: A reported 38 and 67% of Caucasians carry a deletion in both alleles of the glutathione S-transferases M1 (GSTM1) gene, resulting in the total absence of GSTM1 enzyme activity; the GSTM1 null genotype confers an increased risk of lung cancer.28,29 To date, we have considered that genetic changes such as gene deletions and loss of heterozygosity in this region might induce smoking-induced lung cancer development and downregulation of miR-197.