Lehrer S, Levine E, Song HK, Bloomer WD. Breast size, endogenous estrogens, and breast cancer: a review with hypothesis. Mt Sinai J Med 1988;55:142-3.  pdf


Endogenous estrogens probably promote breast cancer only by increasing the amount of glandular tissue within the breast. For this reason, diminished estrogen production in smokers does not protect against breast cancer, though it does protect against uterine cancer. Castration before menopause diminishes breast cancer risk because it reduces prolactin levels as well as estrogen levels.