Stromelysin 3 expression: a useful marker for the differential diagnosis dermatofibroma versus dermatofibrosarcoma protuberans.

Background: Stromelysin 3 (ST3) is a member of the metalloproteinase family, which is expressed in tissue remodeling processes such as scarring, embryogenesis, or tumoral invasion. Although the prognosis of breast cancers and extracutaneous squamous cell carcinomas is correlated with the level of expression of ST3, this staining has not yet found a routine application in dermatopathology.

Objective: Our purpose was to study by immunohistochemistry the expression of ST3 in dermatofibromas and dermatofibrosarcoma protuberans (DFP).

Methods: We selected 40 cases of dermatofibromas, 40 histologically typical DFPs, and 10 giant dermatofibromas. Immunohistochemistry was carried out by means of the LSAB method, with monoclonal anti-ST3 antibody (provided by MC Rio, IGBMC Strasbourg). A semiquantitative scale (0-3) was used to evaluate the level of ST3 expression.

Results: Positively stained cells were observed in all cases of dermatofibromas (100%), including the 10 giant cases, but never in DFP (0%). The staining was intense (class 2 or 3) in 39 of the 50 dermatofibromas. The CD34 staining used as a control proved to be less efficient; 6 DFP were CD34 negative, whereas some of the dermatofibromas showed a marginal CD34 positivity.

Conclusion: Our results are consistent with those obtained by in situ hybridization in previous studies of smaller series of fibrous tumors. The study of ST3 expression in fibrous tumors of the skin shows that this immunostaining could be a useful tool in the purpose of differentiating DFP from giant or invasive dermatofibromas. Although ST3 is a "negative" marker for DFP and therefore does not demonstrate the margins of the neoplasm, it is more reliable than CD34 staining in differentiating this tumor from a dermatofibroma.