Risk factors in breast cancer.

Various factors have been found to be predictors of the relative risk of breast cancer (Table 2). Epidemiologic variables influencing breast cancer risk include age, marital status, geographic location, racial or ethnic extraction, and socioeconomic status. The risk of developing mammary carcinoma is increased with advancing age, among unmarried women, in the United States and Europe, and among women of higher socioeconomic classes. Conversely, a decreased breast cancer risk is observed among fertile married women in Asian countries, among Oriental women, and in lower socioeconomic classes. Reproductive history plays an important role in determining breast cancer risk. The risk of developing mammary carcinoma is increased by an early menarche and decreased by delayed first menses. A late natural menopause increases breast cancer risk while an early oophorectomy offers protection. Hormonal factors are thought to play important roles in the etiology of breast cancer, but the contributions of estrogenic and androgenic influences to mammary neoplasia have not been delineated. Certain estrogen fractions have been implicated as mammary carcinogens, while certain adrenal androgenic steroids have been shown to be promotors of breast cancers. Chronic cystic mastitis is associated with an increased breast cancer risk. A positive family history increases the risk of developing mammary carcinoma and a past history of breast cancer markedly increases the possibility of subsequent breast neoplasia.