The role of hormones in the etiology of breast and endometrial cancer.

Despite many years of extensive investigation, there has been neither a clear-cut pattern of hormonal production nor milieu found in women with breast cancer. Estrogen replacement therapy for menopause does not significantly increase the risk of breast cancer and one study indicated that estrogen users have a lower incidence of breast cancer than that observed in untreated women. Some studies have shown that the mortality rate from breast cancer is lower in estrogen-treated postmenopausal women. Only one investigator has found any significantly increased risk of breast cancer in oral contraceptive users. In that report, increased duration of birth control pill use decreased the risk of breast carcinoma. Several studies were unable to find an increased risk of breast cancer from oral contraceptives while one investigation observed a lower incidence in birth control pill users than that expected. The mortality from carcinoma of the breast in oral contraceptive users was lower than in non-users, most likely due to earlier detection. Although some retrospective studies have indicated that estrogen use increases the risk of endometrial cancer, a prospective investigation found only an insignificant increase. Progestogens afford some protection from cancer in estrogen-treated postmenopausal women. The incidence of endometrial adenocarcinoma is lower than that observed in untreated postmenopausal women. Combination oral contraceptives are protective against developing adenocarcinoma of the endometrium but sequential birth control pills may afford less protection.