Bone, giant cell tumor of: A tumor of bone characterized by massive destruction of the end (epiphysis) of a long bone. The site most commonly struck by this tumor is the knee -- the far end of the femur and the near end of the tibia. The tumor is often coated by new bony growth. It causes pain, restricts movement, and is usually cancerous. Treatment is by surgery, usually followed by chemotherapy.
There is no evidence that the tumor cells themselves are capable of bone destruction; instead, the tumor cells stimulate the formation of cells that function like osteoclasts and resorb bone.
The term "giant cell" reflects the fact that osteoclasts are large multinucleate cells (cells with more than one nucleus) that look gigantic when viewed magnified through a microscope.
Giant cell tumor of bone is also often called osteoclastoma, reflecting the long-held incorrect view that the tumor cells are themselves osteoclasts.