Dermatofibroma and dermatofibrosarcoma protuberans: an immunohistochemical study reveals distinctive antigenic profiles.

Recent studies of mesenchymal cells of the dermis using antibodies to factor XIIIa (FXIIIa) and CD34 have demonstrated immunophenotypic heterogeneity amongst the normal resident spindle/dendritic cells of the dermis. These immunohistochemical markers also have been reported to be useful in the distinction between two dermal mesenchymal tumors of uncertain histogenetic origin - the dermatofibroma (DF) and dermatofibrosarcoma protuberans (DFSP). DFs are FXIIIa positive, CD34 negative while DFSPs are FXIIIa negative and CD34 positive. Expression of CD34 may also have histogenetic implications for these cutaneous neoplasms. In order to further study these tumors we studied 13 DFs and 12 DFSPs immunohistochemically using a microwave antigen retrieval technique in formalin fixed, paraffin embedded tissue with antibodies to FXIIIa, CD34, CD45, factor VIII related antigen (FVIII-RA), the Ki-67 antigen (MIB-1 antibody) and the lectin Ulex europaeus. Of the DFs, all 13 were FXIIIa positive; 12/13 were CD34 negative and 1 was strongly CD34 positive. All DFSPs were FXIIIa negative and CD34 positive. One DFSP also contained an area of fibrosarcoma which was negative for both markers. All tumors were negative with anti-FVIII-RA Ulex europaeus, and anti-CD45. MIB-1 staining demonstrated nuclear staining of the tumor cells in both DFs and DFSPs. Image analysis of MIB-1 stained sections revealed a significant difference in mean percent positive nuclear area between DFs (1.16% +/- 0.405) and DFSPs (2.265% +/- 0.963). In summary, FXIIIa reliably distinguished between DFs and DFSPs; however, CD34 immunoreactivity can be seen in DFs. No evidence for vascular or hematopoietic origin of these tumors was found using microwave antigen retrieval and anti-FVIII-RA, Ulex europaeus, or CD45 staining. With microwave enhancement trypsin was not necessary for FXIIIa staining; however, it did not significantly enhance detection of FVIII-RA, CD45, or Ulex antigens. DF and DFSP tumor cells are in the cell cycle as demonstrated by MIB-1 staining and there are significant differences in percent positive nuclear area between these neoplasms, being higher in DFSP compared to DF.