Malignant fibrous histiocytoma

Summary The ultrastructural findings in 17 cases of malignant fibrous histiocytoma (MFH) are described. The tumors consisted of fibroblast-like cells and histiocyte-like cells in different proportions in different cases. Intermediate, undifferentiated, xanthomatous and multinucleated giant cells were also identified. In 12 of 17 cases myofibroblasts were evident. Acid phosphatase activity was detected cytochemically in the Golgi zone, endoplasmic reticulum and lysosomes (GERL) mainly within histiocyte-like cells, in three cases. These observations indicate that the GERL of the tumor cells are engaged in the formation of lysosomes. The polymorphic cellular composition, including undifferentiated cells, lends support to the concept that the MFH originates from a primitive multipotent undifferentiated mesenchymal cell.Supported by Grants-in-aid for Cancer Research from the Ministry of Health and Welfare (52-1), and from the Ministry of Education, Science and Culture (401057) of Japan and by a Grant from the Fukuoka-ken Anti-Cancer Association. 1976Presented at the 69th Annual Meeting of the Japanese Pathological Society on June 26, 1980, Sapporo