The tumor cells are positive for vimentin and focally positive for CD34, CD68, Factor XIIIa, and desmin. cytokeratin, S100, and SMA are negative.
Ultrastructurally, the tumor consists of spindle cells with
irregular cellular borders. The tumor cells have moderate amounts of
cytoplasm that is rich in rough endoplasmic reticulum (RER) and
mitochondria. Some cells have dense bodies near the plasma membrane.
The tumor cells have one large round, oval or irregular nucleus with
one or two prominent nucleoli. Multinucleated or multilobe-nucleated
cells are identified on some sections. No specific organelles,
lysosomes or lipid droplets are present in the cytoplasm of tumor
Diagnosis: most consistent with malignant fibrous histiocytoma