Progestogens are given to diminish the risk of endometrial cancer (ECA) observed with postmenopausal estrogen therapy. The pattern of progestogen administration and number of days that the progestogen is given per month appear to affect ECA risk. We studied the impact of dose of progestogen, specifically medroxyprogesterone acetate (MPA), on ECA risk in a population-based case control study of 647 cases and 1,209 controls, ages 45-74 years. Among women who took a combined hormone regimen with MPA for less thanlO days/mo, the overall adjusted risk of ECA (relative to that of hormone non-users) was 4.2 [95%, Confidence Interval (CI) 2.0,8.9] in those with an MPA dose less than70 mg/mo; and the adjusted risk of ECA was 2.8 (95%, CI 0.9,8.6) in those with a hi^ier monthly MPA dose. Among women who took MPA cyclically for 10-24 days/mo or as continuous combined therapy, the risk of ECA was similar to non-users, irrespective of the monthly dose. Our findings showed that among the combined hormone regimens most commonly used by postmenopausal women in the USA today, monthly dose of MPA bears little or no relation to risk of ECA.
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