GSTM1 null genotype was associated with BC risk only in current smokers (OR 1.80, 95 % CI 1.09–2.97; P = 0.02), but in case of non-smokers and ex-smokers, the estimated risk was similar, although not significant (OR 1.84, 95 % CI 0.93–3.64; P = 0.08 and OR 2.04, 95 % CI 0.95–4.36; P = 0.08, respectively). This evidence concerns the gene GSTM1 and breast cancer.