A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 46-year-old female presents to her primary care physician after noting a lump in her left breast. She reports finding it two months prior to presentation and feels that it has not grown significantly in that time. She denies nipple discharge or tenderness. On exam, she is noted to have a 3-4 cm, rubbery mass in the left breast. Biopsy shows invasive ductal carcinoma that is estrogen receptor positive. Her oncologist prescribes tamoxifen. All of the following are effects of tamoxifen EXCEPT:
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A
Decreased risk of endometrial cancerCorrect. Correct (as the EXCEPT). Tamoxifen acts as an estrogen agonist in the endometrium and INCREASES endometrial cancer risk — it does NOT decrease it.
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B
Increased risk of deep vein thrombosisIncorrect. True. Tamoxifen increases DVT risk through estrogenic effects on coagulation.
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C
Decreased risk of osteoporosisIncorrect. True. Tamoxifen's agonist activity in bone preserves bone mineral density, decreasing osteoporosis risk.
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D
Increased risk of ocular toxicityIncorrect. True. Tamoxifen is associated with ocular toxicity including cataracts and (rarely) retinopathy.
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E
Increased risk of hot flashesIncorrect. Hot flashes are a true side effect of tamoxifen (anti-estrogen effect at the hypothalamus), so it does not belong in the EXCEPT-style answer for an effect that tamoxifen does NOT cause.
↑ Tap an answer to reveal the reasoning
Answer: A. Tamoxifen is a selective estrogen receptor modulator (SERM) that acts as an estrogen RECEPTOR ANTAGONIST in breast tissue (the basis for its use in ER-positive breast cancer) but as an estrogen AGONIST in other tissues, including the endometrium and bone. Recognizing this tissue-specific dual activity is the key to remembering its side-effect profile:
- Endometrium (agonist effect): INCREASED risk of endometrial hyperplasia and endometrial cancer (this is opposite to option A's claim of 'decreased risk')
- Bone (agonist effect): preservation of bone density → DECREASED osteoporosis risk
- Vascular: INCREASED risk of venous thromboembolism (DVT/PE) — estrogen agonist effect on coagulation
- Eye: INCREASED ocular toxicity (cataracts, retinopathy in rare cases)
The question asks which effect tamoxifen does NOT have. Option A (decreased endometrial cancer) is FALSE — tamoxifen INCREASES endometrial cancer risk. All other listed effects are true. Raloxifene, a related SERM, is endometrium-neutral and is preferred when endometrial concern is significant.
**Why each option:**
**A.** Correct (as the EXCEPT). Tamoxifen acts as an estrogen agonist in the endometrium and INCREASES endometrial cancer risk — it does NOT decrease it.
**B.** True. Tamoxifen increases DVT risk through estrogenic effects on coagulation.
**C.** True. Tamoxifen's agonist activity in bone preserves bone mineral density, decreasing osteoporosis risk.
**D.** True. Tamoxifen is associated with ocular toxicity including cataracts and (rarely) retinopathy.