The bones

There are more than 200 bones in the human body. The bones

• Support the body
• Protect parts of the body
• Act as levers and allow us to move

The long bones of the arms and legs are supporting bones. The bones of the rib cage protect the organs of the chest. The skull bones protect the brain.

The end of every long bone in the body is covered in a smooth, shiny tissue called cartilage. Fibrous straps called tendons hold the long bones together. The tendons and cartilage make joints that allow the bones to move smoothly against each other.

Bone is a framework of supporting tissue, called connective tissue. Bone contains minerals such as calcium. This framework gives the bone its strength. Throughout this framework are the bone cells.

There are 3 main types of cells in our bones

• Osteoblasts – build up the bone framework
• Osteoclasts – break down bone
• Osteocytes – are osteoclasts that have become part of the bone framework

These cells work together to maintain the shape, strength and health of the bones. If a bone gets damaged, the osteoblasts make new bone to repair the damage. The osteoclasts break down any extra bone framework that the osteoblasts make. When bone forms, osteoblasts are trapped within it and become part of the framework. They are then called osteocytes. Osteocytes are involved in maintaining the bone structure.

Inside some of the bones of the body is a space that is filled with bone marrow. The bone marrow is where blood cells are made. All blood cells develop from stem cells which are found in the bone marrow.

Primary bone cancer is cancer that has started in the cells of the bones. There are several different types of primary bone cancer, including

• Osteosarcoma
• Chondrosarcoma
• Ewing's sarcoma
• Spindle cell sarcoma
• Chordoma

Osteosarcoma is the most common type. Even so, it is still rare with only about 150 cases diagnosed each year in the UK. The other types of bone cancer are even rarer. There are about 75 cases a year each of Ewing's sarcoma and chondrosarcoma. There is more information about the different types of bone cancer in this section.

When a primary bone cancer starts to grow, the cancer cells multiply and begin to break down the bone. This weakens the bone in that area. Bone cancer cells can break away from the primary bone tumour and travel to other bones, the lungs or other body organs. There they can grow into secondary tumours.

Most people who have cancer cells in their bones actually don't have primary bone cancer. They have cancer cells that have spread into the bone from a cancer elsewhere in the body. This is called secondary cancer. Nearly all types of cancer can spread to the bones. Common cancers that spread to the bones include breast cancer, lung cancer, prostate caner and kidney cancer. So if you have bone cancer that is secondary to breast cancer, the cancer cells in your bones are breast cancer cells.

The type of primary cancer you have is very important. Cancers respond to treatment according to the type of primary cancer. So breast cancer in the bones will respond to treatments for breast cancer.

If you have secondary bone cancer, this is not the right section for you. You need to look at the section for your type of primary cancer – named after the place in your body where your cancer started.