Estrogen therapy and breast cancer in postmenopausal women.

During the 6-year period 1972-77, 123 postmenopausal women with breast cancer either had the disease diagnosed at Wilford Hall USAF Medical Center or were referred there for therapy. Their ages ranged from 33 to 90 (mean, 56.6 years). Of these women 64.2 percent had never taken hormones, 25.2 percent were estrogen users, 4.9 percent were estrogen-progestogen users, 4.9 percent had a history of hormone usage, and 1 patient was using estrogen vaginal cream. In a subgroup of 27 clinic patients (1975-77 period) during 14,548 patient-years of observation, breast cancer was diagnosed for an overall incidence of 185.6:100,000 women per year. Among the 27 patients, the annual incidence of breast cancer was highest in the untreated group at 410.5:100,000 women. In comparison, the incidence in the estrogen users was 137.7:100,000 women-a significant difference (p less than 0.01). The incidence in estrogen-progestogen users was 155.6:100,000 compared with the incidence in the untreated patients; this difference was also statistically significant (p less than 0.05). There was no significant difference in the incidence of breast cancer between the estrogen users (137.7:100,000) and the estrogen-progestogen users (155.6:100,000). These data indicate that estrogen therapy decreases the risk of breast cancer and that, unlike the situation with adenocarcinoma of the endometrium, progestogens do not offer additional protection from breast carcinoma.