How do our genes affect our risk of cancer?

What are genes and DNA?

Each of our cells contains DNA, a molecular manual for building our bodies and keeping them in good working order. DNA is packaged into units called genes, which each instruct different aspects of our cells’ behaviour.

Cancer is caused by faults in certain genes, resulting in cells multiplying out of control. These gene faults accumulate over our lifetimes, and our cells build up many of them before they become cancerous.

Inheriting faulty genes

While we cannot inherit cancer itself, some people are born one or more steps closer to cancer because they inherit faulty genes from their parents.

This doesn’t mean that they will definitely develop cancer. But it does mean that they need to accumulate less DNA damage for this to happen. They are statistically more likely to get cancer and doctors say that they have a ‘genetic predisposition’ to the disease.

Only around 5-10 per cent of cancers are thought to be caused by faulty inherited genes.

Worried about family history

If you are worried about a family history of cancer, you should visit your GP. They will either reassure you that you are not at particularly high risk, or refer you to a clinical genetics centre.

If the centre thinks you are at a high risk of cancer, they will discuss this with you and help you examine your options. These can include genetic testing, increased screening and cancer prevention advice.

Different types of genes

Most of the inherited cancer genes that we know about are ‘high-risk’ genes - they greatly increase the risk of cancer, but are relatively rare.

Many scientists are now focusing on finding subtle genetic variations that have weaker effects but are more common. Together, these ‘low-risk’ variants could be very important in determining overall cancer risk.

How do I know if I am at risk?

There is a possibility that cancer may run in your family if on one side of the family:

there are several cancers of the same type
there are several cases of rare cancers
members developed cancer before the age of 50
members developed multiple cancer tumours (for example in both breasts)

Clinical genetics centres

In the UK there are 26 NHS clinical genetics centres, most with an associated family cancer clinic. If your doctor refers you to a clinical genetics centre they will asses your risk based on the details of your family history. The clinic will be able to tell many people that they are not at high risk of cancer at this stage.

If the clinic thinks you are at a high risk of cancer, they will discuss this with you and help you examine your options. Options may include genetic testing, increased screening and cancer prevention advice.

Can we do anything about things that are ‘in our genes’?

Absolutely - our genes interact with our environment and lifestyle to affect our risk of cancer.

This means that people who inherit faulty genes that predispose them to cancer can sometimes take steps to reduce their risk of the disease.

For example, CDKN2A is a high-risk gene for melanoma, a type of skin cancer. People with faulty copies of CDKN2A are five times less likely to develop melanoma in the UK than in Australia, a sunnier country. So in this case, sun exposure clearly makes a crucial difference.

How do genes and lifestyle choices interact?

Our genes can alter our risk of cancer by changing the effects of our lifestyle choices.

Some genes neutralise toxic chemicals. Faulty versions of these could make people more vulnerable to the poisons in tobacco smoke and increase their risk of lung, bladder and other cancers.

Other genes control how we process chemicals in our food and could influence how our diet affects our cancer risk.

Genes could even make us more likely to adopt less healthy lifestyles that eventually increase our risk of cancer. For example, genes that make people sensitive to bitter tastes could affect how often they eat vegetables. And genes that make people respond more strongly to the taste, smell or sight of food could lead them to eat more and put on weight.