Giant cell tumor of the bone is a rare, aggressive non-cancerous tumor. It generally happens in adults between ages 20 and 40 when skeletal bone growth is complete. It usually develops near a joint at the end of the bone. The location of a giant cell tumor is often in the knee, but can also involve the bones of the arms and the legs. While the exact cause of giant cell tumors remains unknown. Symptoms may include joint pain, swelling, and limited movement. The goal for treatment of a giant cell tumor is to remove the tumor and prevent damage to the affected bone. Tumors that can’t be removed surgically can often be controlled and sometimes destroyed with radiation therapy. Credit: HopkinsMedicine.Org