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How inherited genes cause cancer

This page is about how genes cause cancer. There is information about


How genes can cause cancer

Cancers develop from a single cell. This happens when there is a fault in one or more of the genes in that cell. Usually a cell must have 6 or more gene faults before it becomes cancerous. Scientists call gene faults ‘mutations’. A gene mutation can make a cell stop working properly. It may become cancerous and divide and grow uncontrollably. These changes can happen either by developing gene faults during your lifetime or inheriting a cancer gene. This section  is about inherited cancer genes

Most cancers are caused by gene faults that develop during our lifetime. There may be a random mistake when a cell is dividing. Or the cell’s DNA may be damaged by a carcinogen. A carcinogen is something that increases the likelihood of a cancer developing – for example, cigarette smoke.


Inheriting a cancer gene

Some people have an increased risk of some types of cancer because they already have a gene fault when they are born. They won’t necessarily develop cancer. But they are one step further along the road to developing cancer than people without that gene fault.

Inherited gene faults that increase the risk of cancer are often in genes that repair mistakes in other genes. The BRCA1 gene that increases the risk of breast and ovarian cancer is a DNA repair gene.

The faulty repair gene doesn’t work as it should. So it doesn’t repair the other genetic mistakes that we all gather as we go through life. In turn, this means you are more likely to gather enough mistakes to cause a cancer at a younger age.

We inherit genes from both our parents. If one of your parents has a gene fault you have a 1 in 2 chance (50%) of inheriting it. The more distant your relative with a gene fault is, the lower your chance of inheriting it.


Why cancer genes don’t always cause cancer

Generally, a cell must gather about 6 specific genetic faults before it becomes cancerous. So being born with one gene fault doesn’t mean you will definitely get cancer. You are at a higher risk than someone without that gene fault because genetically you are one step further down the road to getting cancer. Doctors call this having a genetic predisposition to cancer.

Different gene faults increase the risk of different cancers. With a known gene fault, your doctor may suggest that you need regular monitoring for particular cancers.


The likelihood of a cancer gene causing cancer

Some inherited cancer genes are more likely to cause cancer than others. This varies between cancer genes. It depends on how big a part the gene plays in the development of that cancer. People who have the faulty breast cancer gene BRCA1 have a higher risk of developing ovarian cancer than those with a faulty BRCA2 gene. So this tells us that the BRCA1 gene fault plays a bigger part in causing ovarian cancer than BRCA2.

As well as a gene fault, many other factors need to be in place for a cancer to develop. Because the other factors are not always in place, ‘inherited’ cancer may seem to skip a generation. A parent may have the gene and not get cancer, but their child who inherits the same gene does. We need more research to find out what these other factors are for each type of cancer. And how genes work together to cause cancer to know how we can reduce the risk of developing it. Hopefully in the future we may be able to prevent it altogether.

You can find out more about the causes of cancer in the about cancer section.

If you have a faulty gene your doctor may be able to give you an idea of how much your risk is increased compared to the general population.

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Updated: 15 August 2013