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

To assess an estrogenic effect of tamoxifen on the uterus and to evaluate the usefulness of transvaginal ultrasonography for identifying tamoxifen-induced endometrial pathology.

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 > or = 6 mm (double-layer) was used as cut-off point for further hysteroscopic and histologic examination.

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 cm3 versus 72 cm3; 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.

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.