Bednár tumor associated with dermal melanocytosis: melanocytic colonization or neuroectodermal multidirectional differentiation?

Background: Neuroectodermal differentiation or melanocytic colonization are the opposing theories of histogenesis for the Bednar tumor or pigmented dermatofibrosarcoma protuberans (DFSP). Observation: A 31-year-old African-American woman presented with a 2-cm blue-black shoulder nodule of 1-year duration. Punch biopsy revealed a CD34+, Factor XIIIa-DFSP, harboring numerous, pigmented spindle S100+, Mart-1+ and HMB-45+ cells. Subsequent wide excision demonstrated pigmented dendritic and spindled cells widely scattered throughout the dermis of the 3-cm excisional margins and punch biopsy specimens of normal skin from both shoulders. This latter process was interpreted as dermal melanocytosis (nevus of Ito). The dermal pigmented spindle cells were Mart-1+ and CD34−, and were associated with non-pigmented CD34+, cytologically banal spindle cells, which were more numerous in the excisional margins than the contralateral shoulder. Conclusion: Reported herein is a singular case of Bednar tumor associated with dermal melanocytosis. Although the coexistence of these processes implicates colonization of the DFSP by constituent dermal melanocytes, the mixed immunophenotype (CD34+ or Mart-1+ cells) of dispersed dermal spindle cells hints at the possibility of a common cell of origin: the putative neuromesenchymal cell. In effect, the Bednar tumor could represent one part of a spectrum of neural crest-derived dermal tumors that includes dermal melanocytosis, cellular blue nevus and conventional DFSP.