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What's known on the subject? and What does the study add?Bladder cancer susceptibility may be determined by genetic differences in the activity of glutathione S-transferases, enzymes that regulate the conversion of exogenous carcinogens to excretable hydrophilic metabolites by glutathione conjugation. The discrepancy of results regarding the association of common genetic polymorphisms and complex diseases such as cancer has raised scepticism in this area of research. Although the evidence generally supports the implication of GSTM1 and GSTT1 polymorphisms in bladder cancer, there is still some debate, with some studies in favour and some against.This study shows a greater risk of bladder cancer in individuals with GSTM1 null genotype, particularly women. This relationship is less evident with GSTT1 null genotypes. Null genotypes in both genes appear to be synergistic, particularly among smokers, and to increase the predisposition to more aggressive tumours. Nevertheless, the role of GSTM1 and GSTT1 polymorphisms in predisposition to bladder cancer should be viewed with caution, due to the multifactorial genetic origin of this condition and the need for long-term longitudinal studies to confirm these results.To estimate the prevalence and importance of GSTT1 and GSTM1 genotypes (implicated in glutathione S-transferase activity) in bladder cancer, to determine whether smoking and occupational factors influence this relationship, and to identify the value of GSTT1 and GSTM1 genotypes as prognostic factors.A cross-sectional study was conducted with a group of patients with bladder carcinoma and a control group with benign conditions and no history of tumours. The controls were selected and paired as subjects were recruited.Sociodemographic variables, smoking, professional occupation, histological features and the presence of GSTT1 and GSTM1 polymorphisms by multiplex PCR techniques were assessed.GSTM1 genotypes were investigated in 201 patients and 193 controls and GSTT1 genotypes in 190 patients and 163 controls.In the patients group, GSTT1 null genotype was observed in 22.1% (not significant) and GSTM1 null genotype in 54.2% (P= 0.008) (odds ratio, OR, 1.7); when considered together, 15.5% (P < 0.05; OR, 3.5) of patients had both null genotypes. In the multivariate analysis, the presence of GSTM1 null genotype remained in the model (OR, 2.1) in addition to smoking and age.Subjects with bladder tumour and GSTM1 null genotype were younger than patients without gene deletion (P= 0.049).Women with GSTM1 null genotype presented a higher OR than men (P= 0.024). When stratified by smoking habit, smokers with both null genotypes showed an OR of 4.7.The percentage of patients with G3 tumours was higher in patients with GSTT1 null genotype (P= 0.013) and in patients with both null genotypes (P= 0.002).A higher percentage of infiltrating tumours was also observed in patients with both null genotypes (P= 0.035).The data obtained in the present study suggest a higher risk of bladder cancer in individuals with the GSTM1 null genotype.This risk is twofold higher when GSTM1 and GSTT1 null genotypes are both present and is also higher in smokers.A greater predisposition for more aggressive tumours appears to exist, particularly when both null genotypes are combined.Longer-term longitudinal studies are needed to confirm these results.