Squamous Cell Carcinoma — SCE Dermatology MCQ

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ModerateSkin CancerSquamous Cell CarcinomaSCE Dermatology

A 45-year-old man presents with a 3 cm solitary keratoacanthoma-like nodule on his forearm that has been present for 4 months without regression. What feature makes this lesion most likely to be a well-differentiated SCC rather than a true keratoacanthoma?

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Correct answer: B — Duration >4 weeks without signs of regression

While keratoacanthoma typically undergoes spontaneous regression over 4-6 months, persistence beyond this period without involution favours a diagnosis of well-differentiated SCC. KA and well-differentiated SCC exist on a spectrum and cannot always be reliably distinguished clinically or histologically. BAD guidelines recommend excision of all KA-like lesions because: (1) clinical distinction from SCC is unreliable; (2) biopsy may not sample the full lesion; (3) even if KA, regression leaves a scar. The rapid initial growth and crateriform architecture are shared features that do not distinguish the two.

Reference: BAD 2020 SCC Guidelines; BJD 2015