How does cancer begin?

Cancer begins with an alteration to the structure of the deoxyribonucleic acid (DNA) that is found in all human cells. This is known as a genetic mutation. The DNA provides the cells with a basic set of instructions, such as when to grow and reproduce. The mutation in the DNA changes these instructions so that the cells carry on growing. This causes the cells to reproduce in an uncontrollable manner, producing a lump of tissue, known as a tumour.

How does cancer spread?

Most cancers grow and spread to other parts of the body via the lymphatic system. The lymphatic system is a series of glands (or nodes) that are spread throughout your body, much like your blood circulation system. The lymph glands produce many of the specialised cells that are needed by your immune system.

Bone cancer is somewhat unusual in that as well as spreading via the lymphatic system it can also spread via the blood. This is why bone cancer often spreads to the lungs as cancerous cells can leak out of the bone into the blood and then travel into the lungs.

Known risk factors

Bone cancer is a poorly understood condition and, as a result, only a small number of risk factors for the condition have been identified. These are outlined below.

• Previous exposure to high doses of radiation, such as undergoing radiotherapy; however, the increased risk that is associated with radiotherapy is small.
• Having Pagets disease which is an uncommon bone condition that causes weakening of the bones. Around 1 in a 100 people with the condition will develop bone cancer in later life.
• Having a rare genetic condition known as Li-Fraumeni syndrome.
• Having a previous history of retinoblastoma, which is a rare type of childhood cancer that develops in the eye.

Research has also found that babies who are born with an umbilical hernia are three times more likely to develop Ewing sarcoma than the population at large. An umbilical hernia occurs in 1-2% of all births and is where tissue pokes through the part of the abdomen near to the navel (belly button). It is thought that as an unborn baby develops, the unknown factors that cause the hernia to develop may also contribute to an increased risk of Ewing sarcoma.

However, the increased risk is still very small in relative terms, as only 1 in 110,000 children with an umbilical hernia will go on to develop Ewing sarcoma.

Possible risk factors

A possible risk factor for osterosarcoma is experiencing rapid bone growth during puberty (a growth spurt). Most teenagers who develop osterosarcoma are taller than average. The possible link between growth spurts and osterosarcoma may also explain why most cases develop in teenagers.

One study found a possible increased risk of osterosarcoma in people whose parents worked in farming during the time that they were conceived – possibly due to an exposure to pesticides. However, the researchers who carried out the study emphasised that it was a small study and research involving a larger number of people is needed to confirm or deny this suggested risk factor.

Diagnosing bone cancer

If you visit your doctor with symptoms of bone pain, it is likely that they will carry out a physical examination of the affected bone. They may also refer you for blood tests which can sometimes be useful in confirming or ruling out other conditions, such as infection, or some types of arthritis.

If no obvious cause can be found, it is likely that you will be referred to an orthopaedic surgeon (a specialist in bone conditions) at your local hospital for further testing.

X-rays

It is likely that the surgeon will arrange a series of X-rays of your affected bone to be taken. X-rays can often detect damage to the bones that is caused by cancer, or new bone cells that have started to grow around the cancer. They are also often useful in determining whether you have primary or secondary bone cancer. X-rays cannot provide a definitive diagnosis of bone cancer, but they can indicate whether further investigation is needed. If your X-rays suggest that you may have bone cancer, it is likely that you will be referred to a specialist centre with expertise in diagnosing and treating the condition.

As bone cancer is very rare, it makes sense to have a small number of specialist centres, rather than spreading resources and trained staff across the whole of the health service.

MRI scan

A magnetic resonance imaging (MRI) scan uses a strong magnetic field and radio waves to produce detailed pictures of the inside of the affected bone. A MRI scan is an effective way of assessing the size and spread of any cancerous tumour inside the bones.

If you need to have a MRI scan, you will lie on your back and a small ‘receiving device’ will be placed behind, or around, the part of your body being scanned. You will then be moved into a large tube where the scan will take place. The procedure usually lasts about 30 minutes. A MRI scan is not painful, but some people may find the process a little claustrophobic. If you sometimes get claustrophobia, you should tell the radiographer (the person who operates the MRI scanner) because they will be able to give you a sedative to help you relax.

CT scan

A computerised tomography (CT) scan involves taking a series of X-rays, and using a computer to reassemble them into a detailed three-dimensional image of your body. CT scans are often used to check if the cancer has spread to your lungs. Chest X-rays may also be taken for this purpose.

Bone scans

A bone scan can provide more detailed information about the inside of your bones than a X-ray. A bone scan involves a small amount of radioactive material being injected into your veins. Abnormal areas of bone will absorb the material at a faster rate than normal bone. Therefore, any abnormal areas of bone that are affected by cancer will show up as hot-spots on the scan.

Biopsy

The most definitive way of confirming a diagnosis of bone cancer is to take a sample of affected bone and send it to a laboratory for testing. This is known as a biopsy.

A biopsy can also determine exactly what type of bone cancer you have, and what grade your cancer is. A grading system is used to describe how aggressive the cancer is, and how likely it is that it will spread, with high grade cancers being the most aggressive. This information is important for planning treatment.

The two ways that a biopsy can be performed are described below.

• A core needle biopsy – is performed under a local anesthetic, and is where using a long, thin needle is inserted into the bone and used to remove a sample of tissue.
• An open biopsy – is performed under a general anesthetic, and is where the surgeon makes an incision in the affected bone in order to remove a sample of tissue.

You may need to have an open biopsy if the results of a core needle biopsy are inconclusive.

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