CD34 expression in desmoplastic melanoma.
BACKGROUND
Primary and metastatic malignant melanoma can simulate various soft tissue tumors, including dermatofibrosarcoma protuberans (DFSP). Expression of CD34, a marker characteristic of DFSP, as well as other spindle cell tumors, has not been previously documented in malignant melanoma.


METHODS
We present here an unusual case of metastatic malignant melanoma with a strong histologic resemblance to DFSP and also CD34 expression.


RESULTS
The patient, a 72-year-old man with a history of an invasive malignant melanoma of the skin of the right lower abdomen, presented with a right axillary mass. Histologic sections revealed intersecting fascicles of spindle cells with nuclear pleomorphism and numerous mitotic figures, diffusely infiltrating the adipose tissue in a pattern closely simulating that seen in DFSP. In other foci, epithelioid neoplastic cells with abundant cytoplasm, prominent nucleoli, nuclear pseudoinclusions, and focal cytoplasmic melanin pigment were seen. The neoplastic spindle cells were strongly labeled by two anti-CD34 monoclonal antibodies. Some of the spindle cells and the majority of the epithelioid neoplastic cells expressed S-100 protein and focally tyrosinase. The tumor cells were negative for HMB-45 and MART-1. Melanosomes were not identified by electron microscopy.


CONCLUSIONS
This case demonstrates the potential of melanoma to simulate DFSP closely, on both morphologic and immunohistochemical grounds, and confirms the utility of employing a broad panel of immunohistochemical reagents in problematic cases.
Hoang
M P
MP
Department of Pathology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9073, USA. mai.hoang@UTSouthwestern.edu
Selim
M A
MA
Bentley
R C
RC
Burchette
J L
JL
Shea
C R
CR
D018952:Antigens, CD34 / Q000032:analysis*; D014408:Biomarkers, Tumor; D018223:Dermatofibrosarcoma / Q000737:chemistry / Q000473:pathology*; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D008545:Melanoma / Q000737:chemistry / Q000473:pathology*; D012878:Skin Neoplasms / Q000737:chemistry / Q000473:pathology*; D012983:Soft Tissue Neoplasms / Q000737:chemistry / Q000473:pathology
D018952:Antigens, CD34; D014408:Biomarkers, Tumor