Malignant fibrous histiocytoma: an ultrastructural study of six cases.

The ultrastructures of six malignant fibrous histiocytomas were studied. The lesions were composed of different proportions of fibroblastic- and histiocytic-appearing cells. Intermediate, undifferentiated, and foam cells also were present. Three of the lesions had some "fibroblasts" that had intracytoplasmic bundles of filaments with focal densities (myofibroblastic cells). Malignant fibrous histiocytoma is considered a sarcoma that has an undifferentiated mesenchymal cell origin, that differentiates along a broad fibroblastic and histiocytic (fibrohistiocytic) spectrum, and that usually has a predominant "fibroblastic" component.