Endometrial effects of exemestane compared to tamoxifen within the Tamoxifen Exemestane Adjuvant Multicenter (TEAM) trial: Results of a prospective gynecological ultrasound substudy

ObjectivesThis study prospectively assessed the effects of exemestane and tamoxifen on the endometrium in patients receiving adjuvant treatment for postmenopausal hormone receptor-positive breast cancer within the Tamoxifen Exemestane Adjuvant Multicenter (TEAM) trial.MethodsPatients were randomized to receive tamoxifen or exemestane. In a prespecified trial subprotocol, patients underwent transvaginal ultrasound to assess endometrial thickness at baseline and during a 1- to 3-year treatment period.ResultsAmong 143 evaluable patients, there were no cases of endometrial thickness > 10 mm with exemestane, vs. 11 cases with tamoxifen (p < 0.0003). There was a significant difference between the treatment groups regarding time to endometrial thickness > 10 mm, in favour of exemestane (p < 0.0001). Time to endometrial thickness > 5 mm was significantly longer for exemestane than for tamoxifen (p < 0.0001). Median time to endometrial thickness > 5 mm or censoring was 583 days in the exemestane group versus 315 days in the tamoxifen group. There were also significantly fewer incidences of endometrial thickness > 5 mm at month 6 and month 12 with exemestane compared to tamoxifen (tamoxifen: 6% and 2%; exemestane: 29% and 39%, respectively). After 12 months, mean increases in endometrial thickness from baseline were 2.64 mm and 6.0 mm in the exemestane and tamoxifen groups, respectively (p < 0.0006). Moreover, 17 histologically confirmed endometrial changes were observed in the tamoxifen group, vs. one in the exemestane group.ConclusionsExemestane was associated with significantly less endometrial thickening than tamoxifen during adjuvant endocrine therapy for postmenopausal hormone receptor-positive breast cancer.