A 36-year-old woman was seen for a long-standing pigmented lesion on her left shoulder. Physical examination revealed an infiltrated lesion of 2cm in diameter, with a firm consistency on palpation (Fig. 1A). With a clinical differential diagnosis of congenital melanocytic nevus versus dermatofibroma, we performed surgical excision of the lesion. The histopathology diagnosis was Bednar tumor.

Figure 1

(0,26MB).

Bednar tumor is a rare pigmented histopathological variant of dermatofibrosarcoma protuberans (DFSP). Clinically it is usually indistinguishable from typical DFSP, although, depending of the amount of melanin in the lesion, pigmentation can affect the whole lesion or be a minor histologic finding (Fig. 1B). The main histopathologic feature of Bednar tumor is the presence of a subpopulation of dendritic cells with a greater or lesser proportion of melanin (Fig. 1C). These pigmented dendritic cells are interspersed between the spindle-shaped cells that make up the tumor. They are positive for S100, while the spindle-shaped cells are positive for CD34 and negative for S100, as found in DFSP. It is not known whether these dendritic cells form part of the true neoplastic component, or whether they represent colonization of the neoplasm by melanocytes from the dermoepidermal junction or from the hair bulb (Fig. 1D).