The cytogenesis of macrophages and osteoclast-like giant cells in bone tumors with special emphasis on the so-called fibrohistiocytic tumors.

Recent investigations have suggested that osteoclasts and osteoblasts belong to different cell systems: osteoclasts originate from hemopoietic stem cells, most probably via precursors of the mononuclear phagocyte system. Osteoblasts, however, arise from local mesenchyme. The present classification of bone tumors issued by the WHO, however, is still based on the assumption of osteoclasts and osteoblasts being merely different manifestations or differentiations of the same basic cell type. Consequently, histiocytes or macrophages as well as osteoclast-like giant cells are interpreted in most bone tumors as an autochthonous component of the tumor. In the present study, this theory is contradicted by histological immunohistological, electron microscopic, and autoradiographic-electron microscopic results on a larger number of osteosarcomas, chondromas, chondrosarcomas, chondroblastomas, aneurysmal bone cysts, giant cell tumors of bone, malignant fibrous histiocytomas, fibrosarcomas, desmoplastic fibromas, Ewing's sarcomas, fibrous dysplasias, nonossifying fibromas, and malignant hemangioenkdotheliomas of bone. In order to elucidate the role of macrophages and osteoclast-like giant cells, different monoclonal antibodies were applied to bone tumor specimens as markers of mononuclear macrophages and giant cells. The concept of what is called fibrohistiocytic tumors should be reconsidered. Immunohistological studies have shown that in malignant fibrous histiocytoma as well as in giant cell tumors of bone only a certain portion of macrophages will react with the highly specific antibodies, whereas the majority of tumor cells are negative. This finding alone suggests that the infiltration of macrophages is a reactive phenomenon. It is in agreement with earlier autoradiographic and electron microscopic investigations on giant cell tumors of bone, confirming that only the fibroblast-like tumors are actually proliferating. These data were verified in the present study with the aid of double labeling immunohistological techniques, using antibodies against mature tissue macrophages and others against a proliferation-associated nuclear antigen. Only the fibroblast-like cells, which do not react with the macrophage-specific antibody, will express the proliferation-associated nuclear antigen. Analogous results were obtained in malignant fibrous histiocytoma. We may infer from these results that the majority of these tumors must be neoplasms of local mesenchyme, mostly in fibroblastic differentiation, while the considerable number of macrophages is seen as a reactive phenomenon.(ABSTRACT TRUNCATED AT 400 WORDS)