Primary osteosarcoma of the lung: a case report.

We report a rare case of primary osteosarcoma of the lung. A 73-year-old Japanese man with a productive cough and hemosputum was referred to us for further evaluation of a huge cavitating mass in the left upper lobe, shown on a radiograph of his chest. The result of a tumor biopsy, via fiberoptic bronchoscope, raised a strong suspicion of sarcoma. Therefore a left upper lobectomy was performed without any adjuvant therapy. The tumor, which measured 72 x 70 x 62 mm, was well-defined, whitish-yellow in color and soft in consistency. Histological examination of the tumor showed a dense proliferation of spindle cells and the presence of many collagen fibers. Eosinophilic osteoid, with no epithelial structures, were noted in the stroma. Immunohistochemically, the tumor cells were positive for mesenchymal, but negative for epithelial markers. These pathological features suggested the tumor was an osteosarcoma. A general inspection of other organs did not reveal any more tumorous lesions, therefore, the final diagnosis of the tumor was primary osteosarcoma of the lung.