CYP3A4 and breast cancer: Since human guts are the primary tissues that have contact with dietary carcinogens, it is intriguing that digestive cancer risk is not modified by genetic factors that are related to other human cancers such as prostate, breast or lung, thus reinforcing the hypothesis that the association of CYP3A polymorphisms with prostate or breast cancer are related to endogenous substances rather than xenobiotics carcinogens [37-43].