Malignant fibrous histiocytoma: an ultrastructural study of eleven cases.

Eleven cases of malignant fibrous histiocytoma were examined electron microscopically. In six of seven cases with storiform-fascicular histologic features and in two cases with a myxoid pattern, no malignant-appearing histiocyte-like cells were identified. The neoplastic cells were fibroblasts and myofibroblasts, occasionally admixed with lymphocytes and benign-appearing histiocytes. Only in the other three cases (two pleomorphic sarcomas and one tumor with a storiform-fascicular pattern) were malignant cells with the features of histiocytes identified. The authors propose that some neoplasms with a storiform-fascicular pattern would be more accurately classified as fibrosarcomas than as histiocytomas and speculate on the possible histogenesis of those tumors that do contain histiocyte-type cells.