Pulmonary malignant fibrous histiocytoma. Light and electron microscopic studies of one case.

A malignant fibrous histiocytoma (MFH) arising in the lungs of a 51-year-old man was studied by light and electron microscopy. Features observed were identical to those of MFHs which occur in the skin and subcutaneous tissue and less commonly in other deep locations. By light microscopy, a storiform pattern with admixture of fibroblasts and histiocytes, as well as xanthomatous and giant cells, was noted. Undifferentiated tumor cells along with fibroblasts and histiocytes in different degrees of differentiation were identified ultrastructurally. These findings lend support to the concept that MFH is a sarcoma of primitive mesenchymal cell origin. The addition of the lung as another primary site for the development of this tumor is consistent with the view that MFHs may potentially arise in any part of the body.