Risk factors for breast cancer. Despite the numerous risk factors for the development of breast cancer that have been investigated, only a few demonstrate a clear association with breast cancer development. Female gender and increasing age are the most important factors, followed by factors involving a woman's menstrual, reproductive, and family history. The risks related to menstruation and reproduction are probably related to the duration of estrogenic breast stimulation. The relationship of family history and breast cancer risk is unclear, but there may be a true genetic basis. The previous occurrence of breast cancer (invasive or in situ), the presence of proliferative pathological changes, especially with atypia, and the presence of other malignancies (e.g., primary ovarian and endometrial cancer) are histological risk factors for the development of new or recurrent breast cancer. Radiation exposure, the use of exogenous estrogens (both estrogen replacement therapy and oral contraceptives), diet (especially fat consumption), and alcohol intake may all play a role in cancer risk. Certain medications as well as patient demographics may also have a weak association. Cigarette smoking, caffeine consumption, and stress presently have little support for an association with breast cancer risk. It should be noted that in only one in four patients can breast cancer be accounted for by the known risk factors. This demonstrates that although presently known risk factors may help in screening for the early detection of breast carcinoma, in its possible prevention by modulation of influenceable factors, and in advising patients about their risks, these factors are merely strong associations with breast cancer incidence and not actual causations. The mechanisms of the development of breast cancer are as yet unknown. 