Menopausal estrogen use and risk of breast cancer.

To assess the relationship of menopausal estrogens to breast cancer risk, the authors conducted a case-control study among 881 cases and 863 controls identified through the Breast Cancer Detection Demonstration Project (BCDDP). Use of estrogens was associated with a relative risk (RR) of 1.24 (95% C.I. 1.0-1.5), with higher risks observed among users of high-dose preparations. Hormone effects predominated among women who received them following bilateral oophorectomy (RR = 1.54), obliterating the protective effect normally associated with the operation. In this group, risk increased with years of estrogen use, reaching risks of 2-3 for users of ten or more years. High risks were also observed among oophorectomized women who used hormones in the presence of other risk factors, including nulliparity, family history of breast cancer, and benign breast disease. These results suggest a possible, although complex, relationship between estrogen use and risk of breast cancer.