Cigarette smoking and the risk of breast cancer in women: a review of the literature.

Animal experiments and in vitro studies have shown that compounds found in tobacco smoke, such as polycyclic hydrocarbons, aromatic amines, and N-nitrosamines, may induce mammary tumors. The findings of smoking-specific DNA adducts and p53 gene mutations in the breast tissue of smokers also support the biological plausibility of a positive association between cigarette smoking and breast cancer, as does the detection of carcinogenic activity in breast fluid. However, epidemiological studies conducted over the past few decades have variably shown positive, inverse, or null associations. To help reconcile the discrepant findings, epidemiologists have paid increasing attention to measures of exposure to tobacco smoke that might be of the greatest etiological importance, to aspects of the smoker that might modify the association between smoking and breast cancer risk, and to the potentially different associations that might exist with different types of breast tumors, such as those with and without estrogen or progesterone receptors. Overall, the results of these studies suggest that smoking probably does not decrease the risk and indeed suggest that there may be an increased breast cancer risk with smoking of long duration, smoking before a first full-term pregnancy, and passive smoking. These findings require confirmation in future studies, as do suggestions of increased risk among women with certain genotypes.