Objective: To investigate the risk of endometrial cancer associated with various regimens of postmenopausal hormone therapy.
Methods: Data from a population-based case-control study were analysed that included 591 women newly diagnosed with endometrial cancer, aged 40-79, and who were reported to Wisconsin's statewide tumor registry in 1991-1994. Similarly aged population controls (n = 2045) were randomly selected from lists of licensed drivers and Medicare beneficiaries. Information on hormone use and other factors was obtained through telephone interviews.
Results: Ever use of estrogen-progestin hormones was associated with increased endometrial cancer compared to women who had never used hormones; the increase per year of use was 7% (95% confidence interval 1-13%). Both cyclic (<10 days per month) and continuous progestin used with estrogen were associated with comparable twofold increases in risk relative to non-users. There was no increased risk associated with progestin used for 10-21 days per month.
Conclusions: Both continuous and cyclic progestin regimens are associated with a much lower risk of endometrial cancer than estrogen alone. However, many women using these regimens remain at significantly increased risk of endometrial cancer.