A tumor is a lump or mass of tissue that forms when cells divide uncontrollably. A growing tumor may replace healthy tissue with abnormal tissue. It may weaken the bone, causing it to break (fracture).

Most bone tumors are noncancerous (benign). Some are cancerous (malignant).Benign tumors are usually not life-threatening. Malignant tumors can spread cancer cells throughout the body (metastasize). This happens via the blood or lymphatic system.