Review of the endometrial effects of estrogens and progestins.

Several controversial areas have been reviewed. It would seem from the evidence at hand that progression from endometrial hyperplasia to endometrial carcinoma does occur in a significant percentage of women and that endometrial hyperplasia, particularly adenomatous hyperplasia and atypical hyperplasia, must be regarded as premalignant changes. Gambrell believes that all stages of hyperplasia should be regarded as premalignant. Previous and retrospective studies provide evidence implicating estrogens in the causation of both endometrial hyperplasia and endometrial carcinoma. Although some of these studies may have design flaws, the amount of data is substantial. Prospective studies have demonstrated an increased risk of hyperplasia in women treated with estrogens. An increased risk of endometrial carcinoma in estrogen users compared with nonusers has been suggested even more recently. Reviewed as a whole, the cumulative evidence provided by these studies clearly supports this association, and it would appear the only issue left to resolve may be the magnitude of the association. Cyclic administration of estrogens may decrease the risk of development of endometrial carcinoma. It would seem, however, that such administration does not totally eliminate risk under any circumstances, and in fact, a dose-related relationship appears to persist. It seems well established that progestogens do decrease the risk of both endometrial hyperplasia and endometrial carcinoma associated with the administration of estrogen to peri- and postmenopausal women. Such reduction in risk is significant and lower relative risks in estrogen/progestogen treated women have been reported compared to untreated women. This reduction in risk has been reported in a variety of studies. Whitehead and co-workers have provided a clear biochemical mechanism for progestogen protection of the endometrium in the antagonism of estrogen at the endometrial cellular level. The evidence at hand in the literature would suggest that progestogens should be administered for at least 10 days per cycle. In summary, there is good evidence that the addition of a progestin to estrogen therapy prescribed for the symptoms of menopause provides protection from endometrial hyperplasia and related carcinoma. The protection conferred is greater than that afforded by cyclical estrogen-alone therapy, and allows for continuous therapy, hereby providing greater symptomatic relief. There is little evidence for adverse effects caused by the added progestins, but further studies of women on combined therapy will undoubtedly be warranted.