Only one study reported the relationship between GSTM1/ GSTT1 double-null genotype and the risk of bladder cancer stratified by smoking status; this study showed that non-smokers with GSTM1/ GSTT1 double-null genotype had an elevated bladder cancer risk (OR=2.66, 95%CI: 1.22–5.81). This evidence concerns the gene GSTM1 and urinary bladder carcinoma.