Giant cell tumor with viral-like intranuclear inclusions associated with Paget's disease.

A case of giant cell tumor (GCT) of the distal femur in a 56-year-old man is reported in association with Paget's disease. The case is unique in that is is the first report of GCT arising in a patient with this disease in which the neoplasm arose in a bone that did not show radiologic evidence of Paget's disease. This case also represents the first example of such an association in which viral-like inclusion bodies are seen in the osteoclast of the tumor. The fact that similar inclusion bodies are seen in the osteoclast of patients with Paget's disease and in their GCT implies a cause-and-effect etiologic relationship rather than mere coincidence. The implications are that a slow-virus infection is involved in the pathogenesis of Paget's disease and in giant cell tumors occurring in patients with this disease.