What causes primary bone cancer?

A cancerous tumour starts from one abnormal cell. The reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply 'out of control'. (See separate leaflet called 'What Causes Cancer' for details.) In most cases of primary bone cancer it is not known why cells become cancerous. The most common types, osteosarcoma and Ewing's sarcoma, mainly occur in young people. The cause of these may have something to do with changes in the bone as it is growing.

In some cases, there is a known 'risk factor'. For example, your risk of developing a primary bone tumour is increased if you have:

• High dose radiotherapy for other problems.
• Paget's disease. This is a disease of the bone which occurs in some older people.
• An osteochondroma (chondroma). This is a benign (non-cancerous) bone tumour which occasionally turns into a chondrosarcoma.
• Certain rare inherited disorders including: Li-Fraumeni syndrome and hereditary multiple exostoses (HME), and hereditary retinoblastoma (a rare childhood cancer of the eye).
• Ollier's disease (enchondromatosis) - a rare bone condition.

What are the symptoms of primary bone cancer?

• Pain. The pain may be quite vague at first, but tends to gradually becomes persistent and more severe over the affected part of the bone.
• Swelling over the affected part of the bone. (May only be noticeable with bones close to the surface of the skin.)
• Difficulty in moving a joint if the cancer is near to a joint.
• Pressure symptoms if the tumour grows from the bone and presses on nearby structures. For example, pressure on a nerve may cause pain, tingling, weakness of muscles, or numbness of an area of skin.
• A break (fracture) of a bone may occur at the site of the tumour after a minor injury.

General symptoms may occur as the cancer becomes larger. For example, tiredness, weight loss, sweats. If the cancer spreads to other parts of the body, various other symptoms can develop.

How is primary cancer of the bone diagnosed and assessed?

Initial assessment and diagnosis
If a doctor suspects that you may have primary bone cancer, you are likely to have a number of tests. These may include one or more of the following:

• An x-ray. Primary bone cancers often have a characteristic appearance on an x-ray.
• A bone scan. A bone scan involves an injection of a a small dose of radioactive material. This is taken up by active bone tissue. Cancerous bone tissue is very active and shows on a scanner as a 'hot spot'.
• MRI scan. This is useful to show the exact site and size of a tumour.
• A bone biopsy. A biopsy is when a small sample of tissue is removed from a part of the body. The sample is then examined under the microscope to look for abnormal cells.

If you are confirmed to have primary bone cancer then further tests are usually advised to assess if the cancer has spread. This may include various blood tests, x-rays and scans.医学全在线www.med126.com

Assessing the severity of the cancer - grading and staging
The results of the biopsy can show the type of the cancer. Also, by looking at certain features of the cells the cancer can be 'graded'. For primary bone cancers, two grades are used.

• Low grade - the cells look reasonably similar to normal bone cells. The cancer cells are said to be 'well differentiated'. The cancer cells tend grow and multiply quite slowly and are not so 'aggressive'.
• High grade - the cells look very abnormal and are said to be 'poorly differentiated'. The cancer cells tend to grow and multiply quite quickly and are more 'aggressive' and are more likely to spread.

The stage of primary bone cancer is based on the grade of the cancer, and how much it has grown or spread. The staging system commonly used is:

• Stage 1A - the cancer consists of low-grade cells, and is totally within the bone. There is no spread to other parts of the body.
• Stage 1B - the cancer consists of low-grade cells, but has grown through the wall of the bone. There is no spread to other parts of the body.
• Stage 2A - the cancer consists of high-grade cells, and is totally within the bone. There is no spread to other parts of the body.
• Stage 2B - the cancer consists of high-grade cells, but has grown through the wall of the bone. There is no spread to other parts of the body.
• Stage 3 - the cancer is any grade but has spread to other parts of the body.

The staging is important as the treatment options and outlook (prognosis) differ depending on the stage of the cancer.

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