Primary malignant fibrous histiocytoma of bone: report of six cases with ultrastructural study and analysis of the literature.

Six cases of malignant fibrous histiocytoma (MFH) primary in bone were studied clinicopathologically with ultrastructural study of three. The histologic differentiation of MFH from osteosarcoma and from fibrosarcoma is discussed. Two of the six cases had highly malignant tumors histologically designated as Grade III and IV; one died with diffuse metastatic disease eight months after diagnosis and the second developed pulmonary metastases within ten months. Review of the literature revealed that 45 of the total 119 reported cases had been followed for less than five years; these cases were considered unevaluable for assessing biologic behavior. The remaining 74 cases, followed for more than five years or until death, showed a 36.5% five-year survival rate. All but one of the cases which developed metastasis within five years did so within the first two years. It is therefore concluded that MFH of bone is a rapidly metastasizing tumor with a relatively low five-year survival rate. Paradoxically, 13 of these 74 cases (17.6%) survived between five and 38 years with no evidence of disease. This is comparable to the long-term survival rate in osteosarcoma. The five-year survival rate is also comparable to that of fibrosarcoma of bone.