The effect of the duration of progestin use on the occurrence of endometrial cancer in postmenopausal women

OBJECTIVE: Women who have ever used estrogen replacement therapy (ERT), even at a low dose, have an increased incidence of endometrial cancer. The addition of a progestin to ERT reduces the incidence of endometrial cancer. The duration of progestin administration is more important than the dose. DESIGN: A MEDLINE review of the literature was performed using the search terms endometrial cancer, epidemiology, and hormone replacement therapy (HRT). RESULTS: Women who have ever used ERT have an increased incidence of endometrial cancer. The use of HRT for more than 5 years, with a progestin use of <10 days per cycle, has a relative risk = 1.8. Continuous combined HRT, or sequential or cyclic HRT with >10 days of progestin per cycle, appears to decrease the incidence of endometrial cancer to that found in nonusers of HRT. CONCLUSIONS: The use of HRT in postmenopausal women with a uterus reduces the incidence of endometrial cancer. The duration of progestin administration should be 14 days or more per cycle based on recent epidemiologic data.