Giant cell tumors of bone.

Giant cell tumors of bone are uncommon primary bone tumors that occur in young adults and predominantly affect the ends of long bones, most notably the distal femur and proximal tibia. The lesion is seen on radiographs as a multilobed lytic defect with a sharply-defined transition zone, cortical thinning and in some instances a trabeculated appearance. The clinical behavior ranges unpredictably from quiescence to marked local aggressiveness with a tendency to local recurrence. The diagnosis depends on obtaining a histologic specimen, which usually shows benign tissue. However, a few apparently benign giant cell tumors of bone are capable of producing distant lesions, especially in the lung. Primarily or secondarily malignant giant cell tumors of bone are exceedingly rare. Treatment relies chiefly on excision of the lesion, which should be as complete as possible since the risk of recurrence is more closely dependent on the completeness of tumor removal than on radiologic and histologic evidence of aggressiveness. Histologic sections show numerous osteoclasts admixed with hematopoietic or mesenchymal mononuclear cells. The mesenchymal cells are the tumorous component of the lesion and induce formation of a large number of osteoclasts.