Primary mesenchymal chondrosarcoma of the lung. A case report with immunohistochemical and ultrastructural studies.

A case of primary pulmonary mesenchymal chondrosarcoma is reported. The tumor occurred first in the lower lobe of the right lung of a Japanese female aged 45. Three years after the first operation it metastasized to the upper lobe of the left lung. The tumors were highly cellular and composed of undifferentiated mesenchymal cells and interspersed islands of well-differentiated cartilaginous tissue. Immunohistochemistry failed to detect S-100 and vimentin in the undifferentiated cells. In contrast, Leu-7 and blood coagulation factor XIIIa were positive in these cells. Electron microscopically, undifferentiated mesenchymal cells had narrow cytoplasm with sparsity of organelles, but no intermediate-sized filaments were detected. In the transitional areas between undifferentiated cells and cartilaginous components, thin intracytoplasmic filaments were sometimes observed in the tumor cells. The differentiation toward cartilaginous cells of undifferentiated mesenchymal cells was suggested by immunohistochemistry and electron microscopy. This is the first case of mesenchymal chondrosarcoma occurring in the lung with long-term follow-up.