A histological and immunoenzymatic study on the histogenesis of "giant cell tumor of bones".

We carried out a prospective histologic and immunoenzymatic study, using lysozyme and AI-antichymotrypsin, of 15 well documented cases of giant cell tumors of bones. The histologic appearance of the majority of the tumors was characterized by great pleomorphism. The predominant histologic patterns could be classified as either fibroblastic or histiocytic. Mitoses were seen exclusively on stromal mononuclear cells. All tumors showed positive marking with both lysozyme and AI-antichymotrypsin. The enzymatic activity was more pronounced in areas of conventional histology and appeared as coarse orange-brown granules in the cytoplasm of many mononuclear and multinucleated giant cells. Enzyme-positive cells were less frequently found in fibroblastic areas of the tumor and especially in areas with minimal differentiation. The results indicate that giant cell tumor of bones may result from the neoplastic proliferation of mononuclear cells which in many areas of the tumor differentiate to either fibroblasts or histiocytes. Thus, giant cell tumor of bones may be analogous to fibrohistiocytic tumors of soft tissues.