Overview

About bones

The human skeletal system is made up of more than 200 bones that protect the internal organs, allow people to stand upright, and attach to muscles that allow movement. Bones are connected to other bones by ligaments, which are bands of tough, fibrous tissue. Cartilage is the tough, fibrous material that covers and protects the joints where bones come together. The cortex is the hard, outer portion of the bone. Bones are hollow and filled with bone marrow, which is the spongy, red tissue that produces blood cells.

Bone is a tissue that consists of collagen (a soft, fibrous tissue) and calcium phosphate (a mineral that helps harden and strengthen the bone). There are three types of bone cells:

• Osteoclasts break down and remove old bone.
  
  
• Osteoblasts build new bone.
  
  
• Osteocytes carry nutrients to the bone.

About bone cancer

Cancer can occur in any part of the bone. Cancer begins when normal cells in the bone change and grow uncontrollably, forming a mass called a tumor. A bone tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body). Even though a benign tumor does not spread outside the bone, it can grow large enough to press on surrounding tissue and weaken the bone. A malignant tumor can destroy the cortex and spread to nearby tissue. If bone tumor cells get into the bloodstream, they can spread to other parts of the body, especially the lungs.

There are different types of bone cancer, including:

• Osteosarcoma and Ewing sarcoma are two of the most common types of bone cancer and mostly occur in children and young adults.
  
  
• Chondrosarcoma is cancer of the cartilage and is more common in adults.
  
  
• Chordoma is a type of bone cancer that typically starts in the lower spinal cord.

Rarely, soft tissue sarcomas begin in the bone, including:

• Malignant fibrous histiocytoma (MFH), which makes up less than 1% of bone tumors and is usually found in adults. The arms and legs, especially around the knee joint, are the most common places for MFH to appear.
  
  
• Fibrosarcoma is also more common among adults, particularly during middle age, and most often begins in the thighbone.
  
  
• Paget’s disease of the bone generally occurs in older adults and involves the overgrowth of bony tissue.

This section contains information about primary bone cancer (cancer that begins in the bone). It is much more common for bones to be the site of metastasis (spread) from other cancers, such as breast, lung, or prostate cancer. For information about cancer that has started in another part of the body and spread to the bone, please see the information for that type of cancer or read a fact sheet on bone metastasis.

Find out more about basic cancer terms used in this section.