A 49-year-old woman taking tamoxifen 20 mg daily after breast conservation asks about her endometrial cancer risk. Which statement is correct?
- A Risk rises roughly two- to threefold due to partial estrogen agonist activity of tamoxifen on the endometrium ✓
- B Tamoxifen reduces endometrial cancer risk through its antiestrogen action on the uterus
- C Risk is unchanged unless the patient also takes hormone replacement therapy
- D Risk returns to baseline within six months of stopping tamoxifen regardless of duration of use
Correct answer: A. Risk rises roughly two- to threefold due to partial estrogen agonist activity of tamoxifen on the endometrium
Explanation
Tamoxifen is a selective estrogen receptor modulator: it antagonises estrogen in breast tissue but acts as a partial agonist in the endometrium, stimulating proliferation. Prolonged use raises endometrial cancer risk approximately two- to threefold, and risk continues to climb with cumulative dose and duration beyond five years. Risk declines slowly after cessation but does not normalise quickly. Screening asymptomatic users is not recommended, but any abnormal bleeding warrants prompt evaluation.
Reference: Williams Gynecology, 3rd ed.
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