A case of soft tissue mesenchymal chondrosarcoma metastatic to skin, clinically mimicking keratoacanthoma.

We report the first case of metastatic involvement of the skin by a soft tissue mesenchymal chondrosarcoma (MS). A 64-year-old man presented 15 months after resection of a 7.0 cm MS from his left forearm with a rapidly growing, erythematous nodule on the left side of the upper lip. The lesion was clinically interpreted as a keratoacanthoma. The histologic appearance was identical to that of the soft tissue MS; an immunohistochemical stain for CD99 was positive. Lung and bone metastases were subsequently documented. Our case expands the differential diagnosis of malignancies with cartilaginous differentiation that can involve the skin.