Keratoacanthoma centrifugum marginatum: a rare atypical variant of keratoacanthoma.

Keratoacanthoma centrifugum marginatum (KCM) is an extremely rare variant of keratoacanthoma (KA), with about 30 cases reported since it was first described in 1962. Clinically, KA is an exoendophytic lesion of 10-25 mm with a horn-filled crater that resolves spontaneously within 6 months. In contrast, KCM is characterized by a larger diameter continuous centrifugal spread, concurrent central atrophy and lack of spontaneous remission. Histologically, KCM is similar to KA, with a central keratin-filled crater, overhanging lips of epithelium, a sharp outline between the tumour nests and stroma, and lack of anaplasia and stroma desmoplasia. We describe a 63-year-old agricultural worker with a 9-month history of a multinodular tumour, 70-75 mm in size, on his right hand. The clinical diagnosis of KCM was confirmed by histological examination. Local radiotherapy proved effective, with no recurrence during a 4-year follow-up.