The effects of tamoxifen on the female genital tract

Tamoxifen has both agonistic and antagonistic effects on the female genital tract, depending on the ambient oestradiol concentration and the menopausal status of the patient. In postmenopausal women tamoxifen has an oestrogen agonistic effect on the vaginal epithelium, the uterine myometrium and the endometrium. It may induce benign cystic hyperplasia of the endometrial stroma and cause an increase in poly formation. The risk of endometrial cancer increases 2-3-fold after an exposure of up to 5 years. In asymptomatic tamoxifen users, gynaecological surveillance is not recommended. However, if there is postmenopausal bleeding, then transvaginal ultrasonography and histology of the endometrium are indicated. Tamoxifen can aggravate hot flushes and have a negative effect on sexual function. In premenopausal women, tamoxifen may induce ovarian cysts resulting in high serum-oestradiol levels. Oligomenorrhoea and amenorrhoea will occur in half of the patients. Tamoxifen has an antagonistic effect on the endometrium in premenopausal women and is associated with hot flushes and impaired sexual functioning. Teratogenic effects on the foetus have been described. Despite its gynaecological side effects, the benefits of tamoxifen in breast-cancer treatment outweigh the risks. Patients need to be informed about these side effects. Irregular or postmenopausal blood loss must always be reported to the treating physician.