Endometrial cancer and estrogen use. Report of a large case-control study.

Our case-control study of the relation between estrogen use and endometrial cancer involved 451 cases and 888 controls. The overall risk of endometrial carcinoma was sixfold for estrogen users as compared with nonusers; long-term users (greater than five years) had a 15-fold risk. Excess risk was present for both diethylstilberstrol and conjugated estrogens. The risk associated with cyclic use was as great as that for continuous use. Increased risk was associated with estrogen use for all histologic grades of the tumor. The risk of advanced-stage carcinoma was fourfold for estrogen users, but rhe confidence interval was wide, and this question requires further study. Finally, this investigation contradicts the speculation that the association between this cancer and estrogen use can be explained by swifter diagnosis for estrogen users, misclassification of estrogen-related hyperplasia or treatment of early symptoms of the tumor with estrogen.