The results suggest that the CYP19 Arg264Cys polymorphism modifies breast cancer risk (OR=1.5, 95% CI=1.1–2.2), especially in association with alcohol consumption (P for interaction=0.04), whereas the CYP1B1 Leu432Val polymorphism appears to play no role here. This evidence concerns the gene CYP1B1 and breast cancer.