Evaluation of endometrial thickness in hormone receptor positive early stage breast cancer postmenopausal women switching from adjuvant tamoxifen treatment to anastrozole.

The aim of this study is to evaluate the effect on sonographically measured endometrial thickness in postmenopausal estrogen receptor positive breast cancer patients with hysteroscopically verified endometrial pathologies who switched from adjuvant tamoxifen (20 mg daily) to anastrozole treatment (1 mg daily). This study included 70 postmenopausal estrogen receptor positive breast cancer patients who switched to anastrozole after tamoxifen; patients had endometrial thickness > 4mm and no endometrial malignancy. Postmenopausal status was defined as cessation of menses for more than 1 year. Endometrial thickness was measured after anastrozole treatment. Patients were on tamoxifen therapy for a variable amount of time, ranging from 1 to 60 months, before switching to anastrozole. Endometrial thickness during anastrozole therapy was lower than after tamoxifen therapy (p < 0.001); the mean reduction in endometrial thickness was 4.5mm (+/-3.0). Cystic endometrial appearance was more frequent in patients under tamoxifen than in those under anastrozole (p < 0.001). Duration of tamoxifen therapy was not correlated to the endometrial thickness at the time of its suspension (p = 0.195). There was a statistically significant correlation between endometrial thickness at the time of tamoxifen suspension and its relative reduction during anastrozole therapy; the reduction was greater in women who had a greater endometrial thickness. A longer duration of tamoxifen therapy was correlated with a greater reduction of endometrial thickness after its suspension. Anastrozole reverses tamoxifen-induced increased endometrial thickness and sonographic endometrial cystic appearance.