Sarcomatoid carcinoma arising in the congenital pigmented nevus after treatment with carbon dioxide snow freezing method.

We report a case of sarcomatoid carcinoma of the skin in a 63-year-old man who was treated with the carbon dioxide snow freezing method for a huge congenital pigmented nevus that extended from the right upper extremity to the right trunk during childhood. He had an exophytic red tumor on the nevus in the right upper extremity that grew slowly for 4 years and rapidly recently. Histological and immunohistochemical studies revealed both epithelial and mesenchymal malignancy in the same tumor. The epithelial component was composed of basaloid cells forming multiple nests with peripheral palisading, positive for keratins and BerEP4, implying basal cell carcinoma. The mesenchymal component was composed of spindle-shaped cells negative for keratins and positive for vimentin, suggesting sarcoma. This is, to our knowledge, the first report of sarcomatoid carcinoma arising in the primary pigmented nevus that had been treated by the carbon dioxide snow freezing method.