Malignant fibrous histiocytoma of the uterus.

A primary, malignant pleomorphic giant cell tumor of the uterus was studied by light and electron microscopy. The tumor was characterized by spindle cells, plump epithelioid cells, pleomorphic giant cells, osteoclast-like giant cells, and foamy xanthomatous cells. Histochemically, tumor cells did not show either myogenic or epithelial characteristics. Immunohistochemically, tumor cells were devoid of evidence of desmin, cytokeratin, myoglobin, and lysozyme (muramidase), but vimentin was weakly positive, and alpha 1-antichymotrypsin was weakly positive in the cytoplasm of pleomorphic giant cells. Ultrastructurally, tumor cells did not show either myogenic or epithelial features, but they resembled a variant of malignant fibrous histiocytoma. The present case was classified as a storiform-pleomorphic and giant cell type of malignant fibrous histiocytoma of the soft tissues. The uterus is considered to be an additional possible site of malignant fibrous histiocytoma.