Transvaginal ultrasonography and endometrial changes in postmenopausal breast cancer patients receiving tamoxifen

Objectives: To assess an estrogenic effect of tamoxifen on the uterus and to evaluate the usefulness of transvaginal ultrasonography for identifying tamoxifen-induced endometrial pathology. Methods: One hundred and two postmenopausal breast cancer patients without gynecological symptoms were examined by transvaginal ultrasonography. Forty-eight patients were treated with tamoxifen and 54 patients served as reference. An endometrial thickness of greater than or equal to 6 mm (double-layer) was used as cut-off point for further hysteroscopic and histologic examination. Results; Thirty percent of the women taking tamoxifen had evidence of an abnormal postmenopausal endometrium compared with 6% in the reference group (P = 0.005). Those patients receiving tamoxifen had a significantly thicker endometrium (median 6.0 mm versus 2.0 mm; P < 0.001), a larger uterine volume (median 93 cm(3) versus 72 cm(3) P = 0.03) and more uterine fluid (12% versus 2%: P = 0.005). Furthermore, an ultrasonographic suspect 'Swiss-cheese' endometrial pattern was noted in almost a quarter of the patients treated with tamoxifen, but this was clearly not associated with intracavitary pathology. Conclusions: Our data indicate that tamoxifen stimulates the uterine body and endometrium. The data also indicate that the ultrasonographic endometrial appearance during tamoxifen therapy may be misleading and that a high percentage (46%) of false-positive results occur. Therefore, in asymptomatic postmenopausal breast cancer patients taking tamoxifen, the findings on ultrasonography should be interpreted with caution.