Objective: To determine the effects of a selective estrogen receptor modulator, raloxifene, on postmenopausal endometrium.
Methods: Healthy postmenopausal women (n = 415) were randomly assigned to one of the following four groups: 60 or 150 mg/day raloxifene hydrochloride, 0.625 mg/day conjugated equine estrogens, or placebo, and treated for 1 year. Endometrial biopsies were obtained in a blinded fashion at baseline and every 6 months after the ultrasound studies. Transvaginal ultrasound, with uterine size measurements, was done at baseline and at 3-month intervals. Saline-infusion sonohysterography was done at baseline and every 6 months.
Results: There were no statistically significant differences in baseline characteristics. Mean endometrial thickness, measured by transvaginal ultrasound, was unchanged from baseline to end point in the placebo and raloxifene groups, whereas in the estrogen group it was significantly thicker by 5.5 mm (P < .001). Mean uterine volume, calculated from transvaginal ultrasound measurements, was higher in the estrogen group only (22 cm3, P < .001). Of the 358 women with paired biopsies, endometrial hyperplasia was present in 2.1%, 0%, and 26.1% of the end-point biopsies in the placebo, raloxifene, and estrogen groups, respectively (P < .001). Proliferative endometrium was present in 2.1% of the end-point biopsies in the placebo group, 1.7% in the combined raloxifene groups, and 39.8% in the estrogen group (P < .001).
Conclusion: Raloxifene, at 60 or 150 mg/day for 1 year, did not stimulate the postmenopausal endometrium. End-point endometrial thickness, morphology, and uterine volume in the raloxifene groups were similar to those observed at baseline and in the placebo group.