• Bernd Gerber, Annette Krause, Toralf Reimer, Ionas Mylonas, Josef Makovitzky, Günther Kundt, and Wolfgang Janni.
• Department of Obstetrics and Gynecology, Klinikum Innenstadt, Ludwig-Maximilians University, Munich, Germany. bernd.gerber@med.uni-rostock.de
• Clin Cancer Res. 2006 Feb 15; 12 (4): 1245-50.

PurposeTo investigate the effect of switching from adjuvant tamoxifen to anastrozole (Arimidex) treatment in postmenopausal women with endocrine-responsive breast cancer and histologically proven tamoxifen-induced benign endometrial pathology.Experimental DesignTwo hundred twenty-six postmenopausal women who had received adjuvant tamoxifen 20 mg/d (> or =12 months, < or =48 months) and developed abnormal vaginal bleeding and/or an asymptomatic endometrial thickness >10 mm [measured by transvaginal ultrasound (TVUS)] were subjected to hysteroscopy and dilation and curettage (D&C). Thereafter, 171 patients were randomized in a phase III study to continue tamoxifen treatment (n = 88) or switch to anastrozole 1 mg/d (n = 83). Patients were monitored for < or =42 months using TVUS at 6-monthly intervals.ResultsAt study entry, there were no significant differences in vaginal bleeding, endometrial thickness, and histologic findings between the two treatment groups. Throughout the treatment period, there was no significant difference in recurrent vaginal bleeding between groups [anastrozole, 4 of 83 (4.8%); tamoxifen, 9 of 88 (10.2%); P = 0.18]. Six months after randomization, the mean endometrial thickness for patients who switched to anastrozole was significantly reduced compared with those who continued tamoxifen treatment (P < 0.0001). Significantly fewer anastrozole patients required a repeat hysteroscopy and D&C compared with those on tamoxifen [4 of 83 (4.8%) and 29 of 88 (33.0%), respectively; P < 0.0001]. Repeat hysteroscopy and D&C revealed endometrial atrophy in all 4 cases in the anastrozole group and 14 polyps, 8 hyperplasias, and 7 atrophies in the tamoxifen group.ConclusionsSwitching from tamoxifen to anastrozole treatment significantly reduced the need for a second hysteroscopy and D&C due to recurrent vaginal bleeding or thickening of the endometrium in postmenopausal breast cancer patients with tamoxifen-induced endometrial abnormalities.

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