Chondrosarcoma with additional mesenchymal component (dedifferentiated chondrosarcoma). II. An immunohistochemical and electron microscopic study.

Light microscopic, immunocytochemical and ultrastructural studies were performed on chondrosarcomas which contained a second, noncartilagenous mesenchymal component. Attention was focused on the nonchondroid portion of each tumor in an attempt to elucidate the histogenesis of this mixed variant of chondrosarcoma. The immunoreactivity of 20 tumors was studied using antisera for S-100 protein, alpha-1-antitrypsin, alpha-1-antichymotrypsin, smooth muscle myosin, desmin, and myoglobin. Cells of the nonchondroid portion stained for alpha-1-antichymotrypsin in 12 of 20 cases, and these were predominantly tumors that had been classified as fibrosarcoma or malignant fibrous histiocytoma by conventional light microscopic study. Staining for S-100 protein was consistently negative, whereas the chondrosarcoma component stained in 14 cases. Six tumors stained for desmin, and four of the six were positive for myoglobin and two for smooth muscle myosin; in four, a rhabdomyosarcomatous component was identified in the hematoxylin and eosin-stained sections. Electron microscopic study was performed on ten tumors and there was a good correlation between the immunohistochemical and ultrastructural findings. Three of the ten were pure rhabdomyosarcomas while the others displayed a range of ultrastructural appearances that can be seen in fibrosarcomas and malignant fibrous histiocytomas. The findings from this study support the view that the tumors are formed by the synchronous differentiation of two separate clones of cells.