A prospective randomised study of transvaginal ultrasound effects of tamoxifen and exemestane in postmenopausal women with early breast cancer.

AIM AND BACKGROUND: A reduction of gynaecological adverse events has been reported in trials comparing aromatase inhibitors with tamoxifen as adjuvant treatment in postmenopausal women with early breast cancer, but there is a paucity of randomised studies specifically investigating their effects on the uterus. We report here the results of a prospective phase III trial comparing the effects of tamoxifen and exemestane by transvaginal ultrasound (TVUS).

PATIENTS AND METHODS: Postmenopausal patients with ER+ early breast cancer were randomised to receive tamoxifen 20 mg once daily or exemestane 25 mg once daily as adjuvant hormone therapy. TVUS was performed at baseline and at 6 and 12 months to measure endometrial thickness (ET) and uterine volume (UV).

RESULTS: A total of 123 women were randomised to tamoxifen (n = 61) or exemestane (n = 62). A significantly higher proportion of patients in the tamoxifen group had increased ET at 6 and 12 months from randomisation compared with the exemestane group (66.1% and 64.3% versus 12.1% and 6.8%, respectively; P < 0.0001). Mean ET and UV also significantly increased with tamoxifen compared to exemestane at both time points (P < 0.01 for all comparisons).

CONCLUSION: Tamoxifen is associated with endometrial thickening and increased uterine volume in a significant proportion of postmenopausal women with early breast cancer. Our study confirms the lack of endometrial effects of exemestane, which may be of interest to patients and clinicians when choosing among adjuvant endocrine options for breast cancer.