Background The distinction between dermatofibroma (DF) and dermatofibrosarcoma protuberans (DFSP) is a well-known challenge for dermatopathologists. Immunohistochemical stains have been used to augment routine histological examination to aid in differentiating DF from DFSP. Stromelysin-3 (ST3) is a member of the matrix metalloproteinase (MMP) family, MMP-11, which is expressed in the skin during wound healing and in the stroma of basal cell carcinoma. Recent studies demonstrated that DFs expressed ST3, whereas DFSPs were only rarely ST3 positive.
Objectives To assess the expression of ST3 in DF and DFSP and to ascertain whether ST3 is superior to factor XIIIa or CD34 in differentiating DF from DFSP, by comparison with factor XIIIa and CD34 expression.
Methods Immunohistochemical staining was performed on 23 cases of DF and 17 cases of DFSP, using antibodies to ST3, factor XIIIa and CD34.
Results ST3 was expressed in all cases of DF (23 of 23) but only one case showed weakly positive staining in DFSP (one of 17). The mean ± SD ST3 immunohistochemistry (IHC) score in DF was 4·52 ± 0·67. The sensitivity of ST3 was 100% and the specificity was 94%. Factor XIIIa was expressed in all cases of DF (23 of 23) and in five of the 17 DFSPs. The mean ± SD factor XIIIa IHC score in the DFs was 4·43 ± 0·73. The sensitivity of factor XIIIa was 100% and the specificity was 71%. CD34 was expressed in four of the 23 DFs and 16 of the 17 DFSPs. The mean ± SD CD34 IHC score in the DFSPs was 4·41 ± 1·37. The sensitivity of CD34 was 94% and the specificity was 83%.
Conclusions Immunohistochemical staining with a commercial anti-ST3 antibody can be successfully carried out in routine dermatopathology. We confirmed that ST3 is a positive marker for DF and that ST3 staining might be more reliable than factor XIIIa staining in differential diagnosis of DF and DFSP. As the present study showed that ST3 was not absolutely negative in all cases of DFSP, the combination with CD34 immunostaining could make the distinction more reliable.