Exogenous hormones, reproductive history, and breast cancer.

We studied 284 patients (20-74 years of age) with carcinoma of the breast and 367 controls; all were admitted to one hospital between 1969 and 1972. The disease was associated with nulliparity, first pregnancy over 20 years of age, premenopausal status, and a lower frequency of artificial menopause. After adjustment for these factors, no significant difference was found between the breast cancer patients and controls in their prior use of either estrogens or oral contraceptives, but the confidence limits on the relative risk, especially for oral contraceptives, were large.