Keratoacanthoma centrifugum marginatum: an unusual clinical and histopathological diagnostic pitfall.

Keratoacanthoma centrifugum marginatum (KCM) is a very rare variant of keratoacanthoma characterized by progressive peripheral growth accompanied by central healing. The tumor has the peculiar ability to involute spontaneously. A careful differential diagnostic with other skin carcinomas or hyperkeratotic lesions is required in order to ensure appropriate clinical management. We report a case of KCM in a 62-year-old man presenting with a solitary, large exophytic, sessile tumor located on the ventral side of the right lower leg, which developed over the course of one year from an initial erythematous papule. The patient presented history of local trauma. To our knowledge, this is the second report in the scientific literature supporting a possible traumatic etiology. Due to its rarity and lack of distinctive histopathological features, KCM poses a difficult diagnostic challenge. Therefore, the importance of an accurate histopathological examination and extensive use of ancillary studies for differential diagnosis is emphasized.