Cancer and the use of estrogens.

Although unopposed estrogen therapy, as well as persistent or increased endogenous estrogens, increases the risk for endometrial hyperplasia and cancer, added progestogen decreases the risk for adenocarcinoma of the endometrium to less than that observed in untreated women. The progestogen challenge test should be administered to all postmenopausal women with an intact uterus--including estrogen-treated postmenopausal women and those with sufficient endogenous estrogens to remain asymptomatic--and the progestogen continued for 13 days each month for as long as withdrawal bleeding results. Estrogen replacement therapy should not be withheld from postmenopausal women who are estrogen deficient, since there is no evidence that estrogens increase the risk for breast cancer. Progestogen added to estrogen replacement significantly reduces the risk for mammary malignancy; therefore, progestogens should be given, even to women who have had a hysterectomy, for 10 to 13 days each month whenever they are prescribed estrogen therapy.