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A prospective study begun in 1976 to determine the incidence of endometrial cancer in postmenopausal women was undertaken because of the adverse publicity alleging an increased risk of endometrial cancer in women receiving estrogen therapy. A retrospective study for the year 1975 was added. During 8,170 patient-years in the 3-year 1975-1977 period, 14 endometrial malignancies were diagnosed, for an annual incidence of 1.7 per 1,000 women. During the 3,792 patient-years of observation of estrogen-progestogen users, the incidence of endometrial cancer was 0.5:1,000. The incidence of this carcinoma among estrogen users (8 cases during 2,088 patient-years) was 3.8: 1,000.The difference between these two groups was statistically significant (p < 0.01).One adenocarcinoma was detected in a patient who used estrogen vaginal cream for 7 months, for an incidence of 1.7:1,000 during 573 patient-years of observation. In the untreated women, during 1,515 patient-years, there were 3 endometrial cancers, for an incidence of 2.0:1,000. There was no significant difference between the untreated group and the estrogen users, and only a trend (p < 0.21) between the estrogen-progestogen users and the untreated women. Synthetic progestogens were used to treat 199 women with endometrial hyperplasia (a precancerous lesion) for 3-6 months. The hyperplastic endometrium reverted to normal endometrium in 96.5 percent. The authors believe that all postmenopausal women with an intact uterus should be given the Progestogen Challenge Test, and the progestogen continued each month as long as bleeding follows. Such methods should be highly effective in preventing most endometrial cancer in these women.Since the mid 1970's, several reports have implicated estrogen replacement therapy in postmenopausal women as a possible cause of endometrial cancer (1-6). These epidemiologic and retrospective studies indicate that in such estrogen

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.

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