TY - JOUR T1 - Effect of Tamoxifen on the Endometrium and the Menstrual Cycle of Premenopausal Breast Cancer Patients JF - International Journal of Gynecologic Cancer JO - Int J Gynecol Cancer SP - 667-681 LP - 667-681 DO - 10.1111/IGC.0b013e3181a47cbe VL - 19 IS - 4 AU - Ciska Buijs AU - Pax H. B. Willemse AU - E. G. E. De Vries AU - Klase A. Ten Hoor AU - H. M. Boezen AU - Harry Hollema AU - Marian J. E. Mourits Y1 - 2009/04/01 UR - http://ijgc.bmj.com/content/19/4/667-681.abstract N2 - 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. ER -