Merkel cell carcinoma — SCE Dermatology MCQ

Correct answer: E — Merkel cell carcinoma

The correct answer is E, Merkel cell carcinoma. A rapidly enlarging (doubled in 6 weeks), painless, firm, red-violet nodule on sun-exposed skin (temple) in an elderly, immunosuppressed patient (azathioprine) fits the classic AEIOU picture for Merkel cell carcinoma: Asymptomatic, Expanding rapidly, Immunosuppressed, Older than 50, UV-exposed site. Merkel cell carcinoma is an aggressive neuroendocrine skin cancer with a strong association with chronic immunosuppression (organ transplant recipients, long-term azathioprine or other immunosuppressants) and UV exposure, and it characteristically presents exactly as described here rather than with a keratotic or crusted surface. Because MCC has high rates of local recurrence, nodal spread and mortality if diagnosis is delayed, any such lesion in an immunosuppressed elderly patient must be urgently biopsied and referred under the two week wait skin cancer pathway. Why the other options are wrong: B. Epidermoid cyst: typically slow growing over months to years, often has a central punctum, and is fluctuant rather than firm; rapid doubling in weeks is atypical. C. Nodular hidradenoma: a benign sweat gland tumour that grows slowly and is not linked to immunosuppression or rapid enlargement. A. Dermatofibroma: a benign fibrous nodule that is stable in size for years, usually on the limbs, and shows the classic dimple sign on lateral pressure, not seen here. D. Sebaceous hyperplasia: presents as small, umbilicated, yellowish papules that are static in size, not a rapidly enlarging red-violet mass. Key point: A rapidly growing, painless, red-violet nodule on sun-exposed skin in an elderly or immunosuppressed patient (AEIOU features) should prompt urgent exclusion of Merkel cell carcinoma via biopsy and two week wait referral.

Reference: British Association of Dermatologists, Skin Health and Disease, Merkel cell carcinoma review, 2021 (https://pmc.ncbi.nlm.nih.gov/articles/PMC9060125/)