CD34 expression in desmoplastic melanoma

Background: Primary and metastatic malignant melanoma can simulate various soft tissue tumors, including dermatofibrosarcoma protuberans (DFSP). Expre ssion of CD34, a marker characteristic of DFSP, as well as other spindle ce ll tumors, has not been previously documented in malignant melanoma. Methods: We present here an unusual case of metastatic malignant melanoma w ith a strong histologic resemblance to DFSP and also CD34 expression. Results: The patient, a 72-year-old man with a history of an invasive malig nant melanoma of the skin of the right lower abdomen, presented with a righ t axillary mass. Histologic sections revealed intersecting fascicles of spi ndle cells with nuclear pleomorphism and numerous mitotic figures, diffusel y infiltrating the adipose tissue in a pattern closely simulating that seen in DFSP. In other foci, epithelioid neoplastic cells with abundant cytopla sm, prominent nucleoli, nuclear pseudoinclusions, and focal cytoplasmic mel anin pigment were seen. The neoplastic spindle cells were strongly labeled by two and-CD34 monoclonal antibodies. Some of the spindle cells and the ma jority of the epithelioid neoplastic cells expressed S-100 protein and foca lly tyrosinase. The tumor cells were negative for HMB-45 and MART-1. Melano somes were not identified by electron microscopy. Conclusion: This case demonstrates the potential of melanoma to simulate DF SP closely, on both morphologic and immunohistochemical grounds, and confir ms the utility of employing a broad panel of immunohistochemical reagents i n problematic cases. (C) Munksgaard 2001.