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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.
3 Answers
Mednet Member
Mednet MemberInvited Expert
Medical Oncology · University of Michigan Medical School
Answered on

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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Mednet Member
Mednet Member
Medical Oncology · Valley Med Onc
Answered on

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

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Mednet Member
Mednet MemberInvited Expert
Medical Oncology · Ohio State University
Answered on

Five-year therapy with tamoxifen is associated with a 1-2% risk of endometrial cancer.

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