Histogenesis of Malignant Giant Cell Tumor and Malignant Fibrous Histiocytoma

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The histogenesis of malignant fibrous histiocytoma (MFH) and giant cell tumor is controversial. To elucidate the cellular origin and characteristics of these neoplasms, we have studied many investigations. The findings of electron-microscopic observation, immunohistochemical study with polyclonal antibody and examination of phagocytosis suggested that the origin of MFH was histiocyte. But they don't have enough specificity to conclusion. In this time, we studied the production of collagen in cell cultures derived from these tumors. As the results, we proved the fact that tumor cells as well as histiocytes produced type III collagen. But as a result of immunohistochemical study of monoclonal antibody, negative reactions for anti-human macrophage, T200, anti-leu-M5, anti-leu-M3 and anti-leu-6 were demonstrated in tumor cells. Furthermore inducers of differentiation was added to the culture, but the results were same. In this method, necessity of a large number of tumor cells became a technical problem. In the study with flowcytometry, all cells which were contained in tumor tissue were divided in two groups according to cell size. The group of bigger cells developed a tendency to contain aneuploid cell and histiocytic cell. Cells with ability of mitosis and histiocytic cells tended to be aneuploid. In the in vivo study, thymus tissue was transplanted into nude mice with human malignant fibrous histiocytoma, Then monotonous histological findings of tumor tissue changed into pleomorphic one composed of inflammatory cells, fibroblastic cells and collagen substance. These findings support the hypothesis that origin of malignant fibrous histiocytoma is histiocyte and a part of histiocytic cells become facultative fibroblasts.