Bednar tumor (Pigmented dermatofibrosarcoma protuberans)

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We report on a 47-year-old Japanese female with Bednar tumor (pigmented dermatofibrosarcoma protuberans) on the right shoulder. Clinically, the lesions were composed of a reddish multilobular, firm nodule which had recurred after surgical treatment 40 years ago, and a black plaque with induration beneath the previous surgical site. Histopathologically, both of lesions were characterized by a proliferation of spindle-shaped cells arranged in a tight storiform pattern, admixed with a small population of melanin-containing dendritic cells. Two types of cells in the tumor were identifiable also by an electron microscopy. The majority of tumor cells resembled fibroblasts charaterized by blongated cytoplasm with developed rough endoplasmic reticula and irregularly shaped nuclei. The other type of cells possessed both melanosomes and premelanosomes, suggesting that the cells have an ability of melanogenesis. Immunohistochemically, most of spindle-shaped cells were positive for CD34 and negative for Factor XIIIa and S-100 protein. The melanin-containing dendritic cells were positive for S-100 protein. There were clusters of Factor XIIIa positive cells adjacent to the melanin-containing dendritic cells. These findings suggest that the melanin-containing dendritic cells may not derived from spindle-shaped cells, and that the Factor XIIIa positive cells may affect the function or activity of the melanin-containing dendritic cells.