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Tamoxifen Endometrial Effects — RACP Adult Medicine MCQ

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ModerateMedical OncologyTamoxifen Endometrial EffectsRACP Adult Medicine

A 55-year-old woman with known breast cancer (ER+/HER2-negative) on tamoxifen develops abnormal uterine bleeding. Transvaginal ultrasound shows endometrial thickness of 15 mm. What investigation is required?

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Correct answer: E — CT pelvis

Tamoxifen has oestrogenic effects on the endometrium and increases the risk of endometrial hyperplasia, polyps, and endometrial carcinoma (2–7 fold increased risk). Any abnormal uterine bleeding in a woman on tamoxifen requires endometrial biopsy (pipelle or hysteroscopy with biopsy) to exclude endometrial pathology. Endometrial thickening on ultrasound alone in an asymptomatic patient on tamoxifen does NOT require biopsy (as tamoxifen-induced subendometrial cystic changes cause spuriously thick appearances on ultrasound).

Reference: Cancer Council Australia – 2024 – Breast Cancer Guidelines; eTG – 2025 – Gynaecology