Porokeratosis Malignancy — SCE Dermatology MCQ

Correct answer: A — Approximately 7-11% lifetime risk of SCC arising within porokeratosis lesions, particularly in linear and disseminated subtypes

Option A is correct: approximately 7-11% lifetime risk of SCC arising within porokeratosis lesions, particularly in linear and disseminated subtypes. Porokeratosis is a disorder of abnormal keratinisation with clonal expansion of atypical keratinocytes at the lesion edge, producing the pathognomonic cornoid lamella; this same clonal instability, compounded by p53 mutations demonstrated in lesional skin, underlies malignant transformation. Widespread, longstanding, linear and disseminated variants carry the highest documented risk, reflecting greater lesional burden, chronicity and field change compared with solitary classic Mibelli-type lesions. This risk justifies patient education and long-term surveillance, with biopsy of any area that becomes indurated, ulcerated, hyperkeratotic or rapidly changing. Why the other options are wrong: C. Only in UV-exposed lesions: UV exposure is a recognised contributory risk factor but transformation also occurs in non-sun-exposed sites (for example linear porokeratosis on the limbs or trunk), so UV exposure is not an absolute requirement for malignant change. D. 0%: this ignores well-documented case series and reviews confirming SCC arising within porokeratosis, particularly in linear and disseminated disease; a zero risk would remove the entire rationale for surveillance. E. 100%: malignant transformation is a minority outcome, not universal; most lesions remain benign throughout the patient's life, which is why active biopsy is reserved for lesions showing suspicious change rather than all lesions. B. 50%: this grossly overstates the published transformation rate, which sits in the single-digit to low double-digit percentage range depending on subtype, not one in two lesions. Key point: Linear and disseminated porokeratosis carry a clinically significant (roughly 7-11%) SCC transformation risk, mandating long-term surveillance and biopsy of any changing lesion.

Reference: DermNet NZ, Porokeratosis, 2023 (https://dermnetnz.org/topics/porokeratosis); supported by Sertznig P et al, Porokeratosis: present concepts, JEADV 2012;26:404-412