Effect of tamoxifen on the endometrium and the menstrual cycle of premenopausal breast cancer patients.

OBJECTIVE

Tamoxifen, a nonsteroidal antiestrogen, is the agent of choice in the treatment of premenopausal receptor-positive breast cancer. This study aimed to investigate the influence of tamoxifen on the menstrual cycle and serum hormone levels and the subsequent endometrial response in premenopausal breast cancer patients.

METHODS

In tamoxifen-using breast cancer patients aged 55 years or younger, the last menstrual period was registered, serum hormone levels measured, and the endometrial response visualized by transvaginal ultrasonography every 6 months. Premenopausal status was defined as serum levels of estradiol (E2) 0.10 nmol/L or more and follicle-stimulating hormone 30 IU/L or less. Premenopausal patients with an endometrial response of greater than 12 mm were offered a hysteroscopy and curettage.

RESULTS

In 121 patients, a total of 241 measurements were performed. Amenorrhea predicted menopausal status incorrectly in 85 (35%) of the 241 measurements in 47 patients. In 8 of 47 endocrinologic premenopausal patients, transvaginal ultrasonography showed an endometrial response of greater than 12 mm (range,15-29 mm). Histopathology in women with an endometrial thickness of greater than 12 mm showed no malignancy. No relation between E2 levels and endometrial thickness was found.

CONCLUSIONS

Tamoxifen leads to a disconnection between clinical and endocrinologic menopause in breast cancer patients aged 55 years or less. In premenopausal patients, tamoxifen has a predominantly antiestrogenic effect on the endometrium without a correlation between E2 levels and endometrial response.