CPC14 Keratoacanthoma in Muir–Torre syndrome: diagnostic confidence enables conservative management

Abstract

Muir–Torre syndrome (MTS) is an autosomal dominant condition characterized by sebaceous neoplasms, multiple keratoacanthoma (KA) or KA at a young age, and internal malignancies. The 5th edition of the World Health Organization (WHO) classification of skin tumours regards KA that typically undergo spontaneous regression as distinct from squamous cell carcinoma (SCC) (World Health Organization. WHO Classification of Skin Tumours, 5th edn. Lyon: IARC, 2025). A 22-year-old man and a 33-year-old woman presented with rapidly enlarging nodules, clinically suspicious for KA, on the nasal alar and upper cutaneous lip, respectively. In the first case, a shave biopsy performed elsewhere was reported as SCC, KA-like. Given the typical clinical KA features, histopathological review was requested and confirmed a well-developed KA, demonstrating wildtype mosaic p16 expression and peripheral graded p53 staining patterns. Despite perineural invasion and involvement of the biopsy base, the patient opted for watchful waiting. The lesion regressed, with excellent cosmesis at 2 months. Subsequent investigation confirmed familial MTS, with a paternal history of colorectal carcinoma at 46 years. The second patient, with known MTS, underwent punch biopsy, which confirmed KA with wildtype p16 and p53 patterns. She similarly elected for close observation. The lesion regressed spontaneously over several weeks, leaving minimal scarring and no adverse cosmesis. These cases illustrate the clinicopathological dilemma of KA in young patients with suspected or confirmed MTS. While excision is frequently performed to exclude SCC, surgery in cosmetically sensitive sites carries morbidity. Improved diagnostic confidence using contemporary histopathological criteria supports conservative management in selected cases with low clinical suspicion for SCC and reliable follow-up. In conclusion, application of current diagnostic paradigms allows broader management options for KA and facilitates appropriate investigation for MTS.