REPLACEMENT ESTROGENS AND BREAST CANCER1

Abstract

The relation between replacement estrogens and breast cancer in menopausal women (age 45–64 years) was evaluated in the Group Health Cooperative of Puget Sound, Washington State, a prepaid health care organization with fully computerized information on outpatient drug use and hospital diagnoses. Little association between current estrogen use and breast cancer was noted in women with a previous hysterectomy (relative risk (RR) = 1.1; 90% confidence interval (Cl), 0.7–1.8). In women with a natural menopause there was a positive association between current estrogen use and breast cancer (RR = 3.4; 90% Cl, 2.1–5.6). This association was strong in naturally menopausal women aged 45–54 years (RR = 10.2) and weaker in the older age group (RR = 1.9).