Recent studies on GST polymorphism have also evaluated the combined effect of GSTM1 and GSTT1 genotypes, but most of them failed to show any significant association between the joint deficiency of these genes and prostate cancer risk [24,26]; to our knowledge, only one study has reported a significant increase prevalence of prostate cancer among carriers of both GSTM1 and GSTT1 null genotypes [27]. This evidence concerns the gene GSTM1 and Familial prostate cancer.