Genetics and cancer risk

Having a family history of cancer doesn’t necessarily increase your risk of developing cancer yourself. Below there is more information on

• Genes and cancer
• Looking at your family history
• Genetic testing
• Reducing your risk

Genes are coded messages in our cells that tell cells how to behave. We inherit our genes from our parents. For a cell to become cancerous, there must be changes in its genes. But most of these gene changes are random, and due to environmental or other factors, and not because we have inherited them from our parents. In fact, inherited faulty genes only cause around 5 to 10% of cancers.

Even when a faulty gene is passed on in a family, it does not mean that everyone in the family will automatically inherit that fault. And if someone does inherit the faulty gene, they may not necessarily develop cancer.

Doctors have identified some of the genes that cause some cancers. These include

• Breast cancer
• Bowel cancer
• Ovarian cancer
• Womb cancer

We know that a family history can increase your risk of developing some other types of cancer. But we don’t know yet which gene causes them. For example, we know that if your father had prostate cancer, you are more likely to develop it at some point in your life. But we need to keep doing more research to find other genes that cause cancer.

Remember - even when several different types of cancer occur in a family, it doesn’t necessarily mean that everyone in that family is more prone to cancer.

To find out if someone has an increased risk of developing a cancer, your doctor will first look at the strength of your family history. They will ask you

• Which family members have had cancer
• The type of cancer they have had
• Their age at diagnosis

There is more likely to be an inherited faulty gene if you have more than two close blood relatives, with the same type of cancer, on the same side of the family. People with inherited cancers also tend to get them at a younger age than normal - usually below the age of 60.

So you will only need to have a genetic test if

• More than two close relatives on the same side of your family have had cancer
• They have had the same type of cancer or cancers that are known to be caused by inherited faulty genes
• The cancers developed when they were young
• One of your relatives has had a genetic test which has found a faulty gene

If you think you might have a family history of cancer, you should see your GP. Remember that cancer happens by chance in most cases, and is not due to an inherited faulty gene. If your GP thinks you might have a faulty gene, they will refer you to a genetic specialist, who will look at your family history in detail. Genetic testing is not straightforward, and it can take months for the results to be available.

To see if a faulty gene runs in your family, a living relative with cancer will need to give a blood sample. A specialist will then look at their DNA to see if there is a faulty gene. If they find one, you can have the test to see if you have that same genetic fault.

Remember - it’s only possible to test for genes that have already been identified - for example the breast cancer genes BRCA1 and BRCA2.

Most cancers are due to a number of risk factors. These vary, depending on the type of cancer. For example, smoking increases your risk of developing lung cancer, but not breast cancer. If you are concerned about cancer, the best thing you can do to reduce your risk is to

• Eat a healthy, well balanced diet
• Take regular exercise
• Not smoke
• Be careful in the sun

As we’ve said, even inheriting a faulty gene won’t necessarily mean you will get cancer. You can still help to reduce your risk by looking at your lifestyle and making sure you keep as healthy as possible. Our reduce the risk website has more information.

There is more information about the possible symptoms of cancer and screening for cancer in our causes, symptoms and prevention section.