The case was previously reported on this journal as a case report of a recurrent pigmented villonodular synovitis of the knee joint. It has been observed for four years after the second operation. There were clinical evidences of malignancy after the second local recurrence, i. e., metastasis to the adjacent lymphnodes and right thoracic cage and retroperitoneal invasion. Pathologically this case was diagnosed as malignant giant cell tumor of tendon sheath.
