Dose of progestin in postmenopausal-combined hormone therapy and risk of endometrial cancer

Objective We studied the impact of progestin dose on this risk. The pattern and number of days per month that progestin is given in postmenopausal combined hormone therapy appears to affect endometrial cancer risk. We assessed the impact of progestin dose on this risk. Study design A population-based, case-control study included 647 cases with endometrial cancer and 1209 controls. Results Among users of estrogen with medroxyprogesterone acetate (MPA) 10 to 24 days/month, women who took >100 mg/month had an endometrial cancer risk that was equal to that of hormone nonusers (95% CI 0.6-1.7). The corresponding relative risk was 0.8 (95% CI 0.5-1.5) in those who used a lower monthly MPA dose for 10 to 24 days/month. Among users of a continuous combined hormone regimen, the risk of endometrial cancer was low relative to hormone nonusers, regardless of MPA dose. Conclusion Among the combined hormone regimens most commonly used by postmenopausal women today, MPA monthly dose bears little or no relation to endometrial cancer risk.