Tumor, malignant giant cell: A type of bone tumor characterized by massive destruction of bone near 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 and restricts movement. 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.
Malignant giant cell tumor, known also as giant cell tumor of bone, has been called osteoclastoma, reflecting the long-held incorrect view that the tumor cells are themselves osteoclasts.