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Breast Cancer • Medical Oncology • NCI-CCC Tumor Board Question • UCLA • HR+ • NCI-CCC Breast Tumor Board Question • Breast Cancer, Non-metastatic
Are pre-menopausal women on tamoxifen at risk for endometrial cancer?
Pre-menopausal women make progesterone and their menses are typically lighter on tamoxifen because it's a mild endometrial ER stimulant blocking their own estrogen from binding the ER.
Answer from: Medical Oncologist at Academic Institution
Analysis of endometrial cancer rates in the NSABP P1 trial in women under age 50, demonstrated a relative risk of 1.42 (0.55-3.81) for tamoxifen that was not statistically significant. Per 1000 women, the rates were 0.82 for placebo and 1.16 for tamoxifen. (Fisher et al., PMID 16288118)
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Answer from: Medical Oncologist at Community Practice
The ACOG position is that Tamoxifen does not increase the risk of uterine cancer in premenopausal women:
https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2014/06/tamoxifen-and-uterine-cancer
Answer from: Medical Oncologist at Academic Institution
Five-year therapy with tamoxifen is associated with a 1-2% risk of endometrial cancer.