MENOPAUSAL ESTROGENS AND BREAST-CANCER

Women [1891] given conjugated estrogens for the menopause were followed for 12 yr (mean) for incidence of breast cancer. Overall, 49 cases were observed; 39.1 were expected on the basis of rates in the general population (relative risk = 1.3, P = 0.06). The relative risk increased with follow-up duration, progressing to 2.0 after 15 yr (13/6.6, P = 0.01). The excess risk after 10 yr was not due to prolonged estrogen use, since there was no clear dose response relation to accumulated years of use. Higher risk accrued to women using higher dose tablets and those taking the medication on an other than daily basis. After 10 yr of follow-up observation, factors related to low risk of breast cancer, multiparity and oophorectomy, were no longer so related. Estrogen use was related to an especially high risk of breast cancer among women in whom benign disease developed after they started the drug.