Effects of long-term estrogen replacement therapy. II. Neoplasia.

Two groups of hypoestrogenic women are analyzed by retrospective comparison. Patients were observed by a single group of physicians for at least five years -- 301 patients treated with replacement estrogen and 309 untreated patients. Of each group, 207 women had uteri in situ. Incidence figures for neoplasia (gynecologic, breast, and all sites) were compared between the two groups and with the Third National Cancer Survey, yielding a risk ratio for the development of adenocarcinoma of the endometrium among estrogen-treated women of 3.8 and 9.3, respectively. There was no increase among any other malignancies. The addition of synthetic progestin to estrogen therapy provided significant protection against the likelihood of developing endometrial cancer and did not reduce previously reported metabolic benefits of estrogen treatment. Data pertaining to estrogen use and details of the patients with endometrial carcinoma are presented.