Identification of Leukocyte-Specific Protein 1-Positive Cells: A Clue to the Cell of Origin and a Marker for the Diagnosis of Dermatofibroma

BACKGROUND Dermatofibroma (DF) comprises a heterogeneous group of mesenchymal tumors, with fibroblastic and histiocytic elements present in varying proportions. The cell of origin of DF has been investigated, but remains unclear. OBJECTIVE The present study attempted to investigate the expression of leukocyte-specific protein 1 (LSP1), a marker of fibrocytes, in DF. Additionally, we evaluated the effectiveness of LSP1 in the differential diagnosis of DF from dermatofibrosarcoma protuberans (DFSP). METHODS Immunohistochemical staining was performed on 20 cases of DF using antibodies against LSP1, CD68, and factor XIIIa (FXIIIa). In addition, the expression of LSP1 and FXIIIa was evaluated in 20 cases of DFSP. RESULTS Eighteen of 20 cases (90%) of DF stained positive for LSP1, with variation in the intensity of expression. CD68 was positive in 10 cases (50%), and FXIIIa was expressed in all cases of DF. There were differences between the regional expression patterns of the three markers in individual tumors. In contrast, only 2 of 20 cases of DFSP expressed LSP1, and none of DFSP cases stained positive for FXIIIa. CONCLUSION The LSP1-positive cells in DF could potentially be fibrocyte-like cells. FXIIIa and CD68 expression suggests that dermal dendritic cells and histiocytes are constituent cells of DF. It is known that fibrocytes, dermal dendritic cells and histiocytes are all derived from CD14+ monocytes. Therefore, we suggest that DF may originate from CD14+ monocytes. Additionally, the LSP1 immunohistochemical stain could be useful in distinguishing between DF and DFSP.