Absence of mononuclear phagocyte antigens in malignant fibrous histiocytoma

Nine malignant fibrous histiocytomas (MFHs) were tested for the presence of macrophage-associated antigens by an alkaline phosphatase-anti-alkaline phosphatase immunohistochemical method. One myxoid and eight pleomorphic-storiform tumors were analyzed with eight antibodies reacting with separate antigens previously found on cells of mononuclear phagocyte lineage. Malignant cells did not react with any of the antibodies, while benign histiocytes within tumor were consistently labeled with all of the antibodies tested. While the malignant cells of MFH previously have been found to share some functional and morphologic properties with histiocytes, they do not possess the surface and cytoplasmic antigens that have been found on various macrophage populations. The malignant cells of MFH are fibroblastic or poorly differentiated mesenchymal cells rather than neoplastic histiocytes.