A Wolf in Sheep’s Clothing: Collision of Melanoma and Keratoacanthoma

Abstract

Collision tumors consisting of melanoma and squamous cell carcinoma are very rare. We present the case of a deceptive hyperkeratotic nodule on the forearm of a 72-year-old woman, which clinically appeared to be a squamous cell carcinoma, keratoacanthoma type. Histological examination surprisingly revealed a coexisting epithelioid melanoma. Thus, this case report shows the importance of an early histopathological and immunohistochemical workup to prevent unnecessary diagnostic and therapeutic delay with negative effects on prognosis.