Dermatofibrosarcoma protuberans treated with Mohs surgery. A case with CD34 immunostaining variability.

Background: Immunohistochemical stains for CD34 antigen can help in differentiating dermatofibrosarcoma protuberans (DFSP) from other fibrohistiocytic tumors and in demarcating its surgical margins during Mohs surgery. However, variable expression of CD34 antigen in nodular areas can sometimes result in negative staining of tissue sections creating diagnostic and therapeutic dilemmas.
Objective: To show the variable expression of CD34 antigen in a DFSP tumor.
Methods: Case presentation of DFSP with immunohistochemical staining using the ABC peroxidase macromolecular complex.
Results: Microscopic examination of paraffin-embedded sections showed CD34-negative DFSP tumor cells with positive staining of endothelial cells. On frozen sections at the time of surgery the tumor cells stained strongly positive for CD34.
Conclusion: This case demonstrates the variable expression of CD34 antigen by DFSP tumors and emphasizes the need to interpret with caution the results of these immunostains during Mohs surgery.