ABSTRACT
<p><b>OBJECTIVE</b>To assess the effect of different schemes of premenopausal tamoxifen therapy on the endometrium.</p><p><b>METHODS</b>Totally 109 normal premenopausal women positive for high-risk factors of breast cancer were divided into two groups, namely periodic and consecutive tamoxifen treatment groups. Endometrial thickness as examined by vaginal sonography was assessed in relation to duration of tamoxifen use and time from discontinuation of the drug.</p><p><b>RESULTS</b>After one year of tamoxifen use, the mean endometrial thickness in periodic treatment group was 6.5-/+1.4 mm, and 10.2-/+2.0 mm in consecutive treatment group. Endometrial thickness increased with the duration of tamoxifen use at the rate of 0.51 mm/year in the periodic treatment group, and 0.73 mm/year in consecutive treatment group. After discontinuation of tamoxifen, the endometrial thickness in the former group decreased by 1.29 mm/year, and by 1.33 mm/year in the latter.</p><p><b>CONCLUSIONS</b>Endometrial hyperplasia is obviously milder in premenopausal women receiving periodic tamoxifen treatment who are at risk for breast cancer than that in women with consecutive treatment. After discontinuation of the drug, the endometrial thickness decreases at a roughly equal slow rate in the two groups.</p>