Dermatofibroma: Unusual lesion with underlying cutaneous horn

Cutaneous horn is a nonspecific clinical description and may arise from a variety of benign and malignant lesions. A 46-year-old Korean man presented with a 1-year history of an extensively hyperkeratotic nodule on his left foot. Following an initial diagnosis of dermatofibroma with underlying cutaneous horn by wedge biopsy, the tumor was completely removed by excision with 5 mm margin. When excisional surgery was performed, the size of the dermal tumor mass was found to be 1.3 cm in length on the axis and 0.6 cm in depth on section. On histopathologic examination, the tumor was characterized by spindle-shaped cells arranged in storiform pattern, epidermal hyperplasia, and an overlying compact hyperkeratotic mass. The tumor cells did not express CD34. Cutaneous horn of dermatofibroma may be the product of epidermis-dermal tumor interaction. Although we performed a wide excision for complete removal of the tumor, Mohs micrographic surgery could have been another option.