Effects of tamoxifen on the female genital tract

Tamoxifen is a widely used drug in medical oncology, mainly for treatment of breast cancer, but also for second line treatment of endometrial cancer. We recently reported an increased incidence of endometrial cancer associated with long-term adjuvant tamoxifen. This observation, previous reports of stimulatory effects of tamoxifen in the female genital tract, and experimental data are in accordance with a mainly estrogenic effect of tamoxifen in these tissues. An increased incidence of endometrial cancer may limit the usefulness of tamoxifen for benign indications. For adjuvant treatment of early breast cancer, however, the improvement of both recurrence-free survival and overall survival probably outweighs the increased frequency of uterine tumors. However, the possibility of growth stimulation of tumor subclones should be considered when tamoxifen is used in the treatment of endometrial cancer.