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Atypical Fibroxanthoma — SCE Dermatology MCQ

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HardSkin CancerAtypical FibroxanthomaSCE Dermatology

A pleomorphic spindle-cell tumour on a sun-damaged scalp extends through subcutaneous fat and shows geographic necrosis. Keratin, S100, desmin and vascular markers are negative. Which classification is most appropriate?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: D — Pleomorphic dermal sarcoma because tumour invasion extends into subcutis

Explanation lettering: D = shown as A · C = shown as B · A = shown as C · B = shown as D

B is correct. AFX is a diagnosis of exclusion for a superficial pleomorphic tumour confined to dermis. Invasion into subcutaneous tissue, tumour necrosis, lymphovascular or perineural invasion supports pleomorphic dermal sarcoma, which has greater recurrence and metastatic potential and requires wider oncological planning. Negative lineage markers help exclude spindle cSCC, melanoma, leiomyosarcoma and angiosarcoma but do not by themselves establish AFX. DFSP is usually a more monomorphic CD34-positive storiform tumour with honeycomb fat infiltration rather than marked pleomorphism and necrosis.

Reference: Primary Care Dermatology Society: atypical fibroxanthoma: https://www.pcds.org.uk/clinical-guidance/atypical-fibroxanthoma