A study on the osseous elements in malignant fibrous histiocytoma of bone.

By studying histochemically and ultrastructurally a case of malignant fibrous histiocytoma (MFH) of bone with neoplastic osteoid elements, the distinction of the tumor from osteosarcoma was discussed. MFH was likely to originate from undifferentiated mesenchymal cells that induced a histiocytic line of differentiation, and some histiocytes seemed to be transformed into well differentiated fibroblastic cells which accordingly differentiated into fibroblasts and osteoblasts. This may explain the existence of the osseous elements in MFH. Sarcoma showing the bimodal--histiocytic and fibroblastic--differentiation should be diagnosed as malignant fibrous histiocytoma, even if it contains tumorous osteoid; it must be clearly distinguished from osteosarcoma, in which the various cells only on a fibroblastic line of differentiation can be identified and the osteoblasts are the predominant cells.