Breast cancer and estrogen replacement therapy.

Concern over the possible effect of estrogen replacement therapy on the subsequent development of breast cancer prompted us to compare 199 postmenopausal breast cancer patients with 451 hospital control subjects and 852 community control subjects on their prior use of estrogens. Estrogen use did not increase the breast cancer risk for women with a surgical menopause. Among women with a natural menopause, estrogens administered by all routes were associated with breast cancer risks of 1.7 of 1.8. There was no coherent pattern of changing risks with varying durations of use, different daily dosages, years since first use of estrogen, or years since most recent use. When women who usually received estrogen by injection were excluded, the risk estimates for oral estrogens were 1.3 (case subjects compared to community control subjects) and 1.2 (case subjects compared to hospital control subjects). These increases were not statistically significant. Use of injectable estrogens produced a fourfold increase in breast cancer risk among naturally postmenopausal women.