Twelve cartilaginous
tumors were studied by electron microscopy and the presence of
S-100 protein was studied immunohistochemically in order to clarify the cell origin of
chondroblastoma, chondromyxoid
fibroma, and
mesenchymal chondrosarcoma. Three
chondroblastomas were characterized by round or ovoid
tumor cells with some cytoplasmic processes, well-developed organelles and thick fibrous laminae in the nuclear membrane, occasional multinucleated giant cells and scanty chondroid matrix.
S-100 protein was demonstrated in the
tumor cells and some multinucleated giant cells Two chondromyxoid
fibromas revealed
tumor cells of varied shapes with characteristic cartilaginous differentiation and abundant chondroid matrix. Spindle
tumor cells showed the ultrastructural features of cartilage cells rather than of fibroblasts and
S-100 protein was also demonstrated in their cytoplasm.
Chondroblastoma and chondromyxoid
fibroma were considered to arise from chondrocytes.
Mesenchymal chondrosarcoma ultrastructurally exhibited round
tumor cells with cartilaginous nature in cartilage islands. Poorly-differentiated portions were composed of primitive round or elongated cells with occasionally admixed round cells with ultrastructural features of cartilaginous differentiation.
S-100 protein was demonstrated in the cells in cartilage islands and in single cells admixed in poorly-differentiated portions. These results support the hypothesis of primitive mesenchymal origin with a tendency to differentiate toward cartilage cells.