disease characterized by uncontrolled growth of cells of the bone. Primary bone cancer-that is, cancer that arises directly in the bone-is relatively rare. In the United States, for example, only about 2,400 new cases of primary bone cancer are diagnosed each year. Most cancer that involves the bone is cancer that has spread (metastasized) from other tissues in the body through the blood or lymphatic systems. Different types of bone tissue give rise to different types of primary bone cancer. Osteosarcoma develops from cells that form the bone, and Ewing tumour of the bone (Ewing sarcoma) develops from immature nerve tissue within the bone. Both types most commonly affect males between 10 and 20 years of age. Chondrosarcoma, which forms in cartilage tissue, principally affects persons over age 50. More than one-half of the cases of primary bone cancer, even once-deadly types, can now be treated successfully.
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