Tamoxifen has different effects on different tissues. Whereas it blocks estrogen in the breast, it has pro- estrogenic effects on bone and in the uterus. Working as an estrogen-like substance, it can cause dysfunctional uterine bleeding and endometrial thickening and very rarely, superficial, easily treatable, endometrial cancer and sarcoma. In a review of all NSABP breast cancer treatment trials, the rate of sarcoma in women treated with tamoxifen was 17 per 100,000 patient years versus none in the placebo group. Similarly, in a separate trial of high-risk women without breast cancer taking tamoxifen as part of a breast cancer prevention trial with a median follow-up of 6.9 years, there were four in the tamoxifen group versus none in the placebo group, translating into a very low risk. This is compared with the incidence of one to two per 100,000 patient years in the general population.
Some women develop endometrial thickening when taking tamoxifen. The significance of endometrial thickening is not clear. At one time, women were regularly subjected to regular screening, ultrasound and even intra-uterine biopsies. Experience had not borne out such an approach. Beyond a routine gynecologic examination eliciting any history of abnormal bleeding, it has been recommended that screening studies and procedures for detecting endometrial pathology in women taking tamoxifen should be left to the discretion of the individual gynecologist. Routine ultrasound screening is not recommended because of significant incidents of false-positive endovaginal ultrasound screening tests. Of course, any abnormal uterine bleeding should be completely evaluated.
There are no guidelines to recommend hysterectomy routinely for patients of tamoxifen. One guideline that has taken up this issue is this Society of Gynecologic Oncology pf Canada and it recommends: “In asymptomatic women on tamoxifen, a routine ultrasound for endometrial thickening should not be performed.” It does not recommend routine hysterectomy.
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