Osteosarcoma arising from giant cell tumor of bone ten years after primary surgery: a case report and review of the literature.

Giant cell tumor of the bone (GCT) is a relatively uncommon tumor. It is characterized by the presence of multinucleated giant cells. GCT is a primary benign tumor but may evolve into a malignant tumor, usually after irradiation. We report a rare case of osteosarcoma arising ten years after the primary surgery for GCT without radiation. A 45-year-old woman presented with severe right knee pain after suffering contusion. Roentgenogram revealed a bone tumor in the lateral femoral condyle of the right knee. Histopathological examination demonstrated the features of GCT, and treatment consisted of curettage and bone grafting. Four months after the operation, multiple lung metastases of GCT occurred, which were treated by partial lobectomy. Ten years after the primary treatment, severe knee pain recurred. Roentgenogram and magnetic resonance imaging (MRI) demonstrated a destructive lesion in the lateral condyle of the right knee. Histopathological examination demonstrated a lacy pattern of osteoids and abnormal mitoses in the aggregated atypical mononuclear cells, indicating osteosarcoma. Despite above-knee amputation and chemotherapy, scapular and lung metastases developed and the patient died five months after above knee amputation. One may question whether the primary GCT contained some malignant cells. However, given the aggressiveness of the malignant tumor, this is unlikely. The recurrence of pain and aggravation of bone destruction many years after the primary treatment suggest malignant transformation of GCT.