CD34 and factor-XIIIa immunoreactivity in dermatofibrosarcoma protuberans and dermatofibroma

The histologic distinction between dermatofibrosarcoma protuberans (DFSP) and the fibrous type of benign fibrous histiocytoma (dermatofibroma, DF) may be extremely difficult. In this study, we evaluated the extent and pattern of immunoreactivity of both CD34 and factor XIIIa in a large number of DFSPs and DFs in order to determine the utility of these markers in their distinction. Using histologic criteria alone, the authors independently evaluated and agreed upon 30 cases of DF and 24 cases of DFSP, and a representative section was stained with antibodies to both factor XIIIa and CD34. Immunopositivity was evaluated semiquantitatively and assigned a score from 0 to 5. CD34 immunoreactivity was seen in 22 (92%) of 24 DFSPs (mean CD34 score, 4.60 +/- 0.3). Only 12 (40%) of 30 DFs showed CD34 immunopositivity (mean CD34 score, 0.6 +/- 0.1). Factor XIIIa was seen in 29 (97%) of 30 DFs (mean factor-XIIIa score, 4.1 +/- 0.3). In contrast, 18 (75%) of 24 DFSPs stained for factor XIIIa (mean factor-XIIIa score, 1.3 +/- 0.2), but in most of these cases the factor-XIIIa-positive cells were felt to be entrapped nonneoplastic dermal dendrocytes. Thus, an immunoprofile using antibodies to CD34 and factor XIIIa is capable of distinguishing between DFSP and the fibrous type of DF in the vast majority of cases, as long as there is recognition that there may be some CD34-positive cells in DFs, as well as some factor-XIIIa-positive cells in DFSPs.