Patterns of postmenopausal progestin use with estrogen in relation to endometrial cancer (United States)

To investigate the risk of endometrial cancer associated with various regimens of postmenopausal hormone therapy.

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.

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.

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.