Giant xanthomatous dermatofibroma - a case distinguished histologically and immunohistochemically from invasive fibrohistiocytic tumors

A 50-year-old woman presented with a skin tumor on her right calf. The tumor had been noticed 20 years previously and grew to more than 60 mm in diameter. The histological findings were characterized by numerous bland xanthomatous histiocytes and a few atypical giant cells with pyknotic nuclei, although mitotic figures were few. These findings led to the diagnosis o f dermatofibroma with unusual xanthomatous expression. Immunohistochemical studies using several markers for histiocytes (lysozyme, α1-antitrypsin. α1-antichymotrypsin and anti- CD68 antibody), anti-factor-XIIIa antibody and anti-CD34 antibody supported the diagnosis.