Enzyme histochemistry of malignant fibroblastic histiocytic tumors. A light and electron microscopic analysis

The enzyme pattern of 13 cases of malignant fibrous histiocytoma (MFH) and 11 cases of myxofibrosarcoma (MFS), a malignant myxomatous soft tissue tumor of fibroblastic histiocytic origin, has been studied. 6 of the 13 MFHs were analyzed enzyme histochemically at the light microscopic level and 7 on the ultrastructural level; of the 11 MFSs 9 were analyzed enzyme histochemically at the light microscopic level and 2 on the ultrastructural level. Differences were observed in the subjectively estimated enzyme activity between low grade MFS and high grade MFS and MFH, and also between histiocyte-like and fibroblast-like tumor cells. Generally a strong reaction of oxidoreductase enzymes (NADH2-diaphorase, NADPH2-diaphorase, glucose-6-phosphate dehydrogenase) and hydrolytic enzymes (acid phosphatase and leucine aminopeptidase) was found in the high grade tumors and was usually higher in the histiocyte-like than in the fibroblast-like cells. Ultrastructurally acid phosphatase occurred predominantly in primary and secondary lysosomes and Golgi zones of the histiocyte-like cells. A strong reaction of alkaline phosphatase was found light microscopically in 2 of 5 MFHs and 5 of 9 MFSs. Ultrastructurally alkaline phosphatase was located along the cytoplasmic membrane of predominantly fibroblast-like cells in 3 of 7 MFHs and 1 of 2 MFSs. The results agree with the concept of two main cell types in MFH and MFS, fibroblasts and histiocytes.