[A case with lung metastasis of osteosarcoma occurred 21 years after the operation of osteosarcoma on left tibia].

The patient was a 38-years-old woman. A chest X-ray film demonstrated the presence of an abnormal lesion. Her past history included osteosarcoma on the left tibia for which she received amputation of the left inferior limb at 17 years of age without any relapse thereafter. Considering that the patient might have lung metastasis of osteosarcoma on the basis of lung biopsy performed under CT guide, and then a tumor was removed under the thoracoscope. The tumor, 2.8 x 2.2 x 2.1 cm in size, was located right under the pleura at left S10 with its inside being filled up with fragile necrotic tissues. When compared pathohistologically with the primary lesion of osteosarcoma which had occurred 21 years before, the lung tumor was almost identical in terms of the tumor cell morphology but had a higher cell density without evidence of osteoid formation. The diagnosis of lung metastasis of osteosarcoma was established on the basis of the clinical course and the immunohistochemical staining. It is extremely rare case that osteosarcoma recurs in the form of lung metastasis 21 years after the operation of primary lesion. We report this case as a valuable one to identify the prognosis of osteosarcoma and the development mechanism of lung metastasis.