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About genes, cancer and family history

There are some important things to understand about how genes are related to cancer. This page has information about

 

What genes are

Genes are coded messages that tell cells how to behave. They control how our bodies grow and develop. We each have about 25,000 genes. So far scientists have found around 300 that play some part in the development of cancer. There is more information about how genes work in the about your body section of CancerHelp UK. And more about how genes cause cancer in our inherited genes and cancer risk section.

 

Difference between ‘inherited’ and ‘non inherited’ cancers

It is important to understand the difference between cancers due to genes you were born with and cancers due to a gene change that have happened during your lifetime.

All cancers develop because something has gone wrong with one or more of the genes in a cell. But most of these gene changes happen during our lives. They happen as we get older or because of something we are exposed to, such as cigarette smoke or sunlight. These substances, called carcinogens, cause changes in the genes that make body cells more likely to become cancerous. These gene changes don’t affect all body cells. They are not inherited and cannot be passed on to your children.

The information in this section is not about gene changes that happen during your lifetime. It is about cancers due to specific inherited ‘cancer’ genes. This is when there is a mistake or a fault in an egg or sperm cell. These can be passed on to children. This is much rarer, but we have written this section about it because people worry about it so much. There is information in each cancer section about other risk factors, which are often much more important.

 

How common are ‘inherited’ cancers?

We hear a lot about people getting cancer because they have inherited a single gene fault that increases their risk. But this is relatively rare. Most cancers develop because of a combination of chance and our environment, not because we have inherited a specific cancer gene. For example, only about 3 in 100 breast cancers (3%) are due to an inherited faulty gene.

This is a fast changing area of medicine. The breast and ovarian cancer genes BRCA1 and BRCA2 were among the first cancer genes scientists identified in the 1990s. Since then researchers have found other genes that increase the risk of other cancers. They will continue to find more over the next few years.

 

What a family history of cancer is

Many people with cancer in the family worry that they are at greater risk of getting it themselves. But as we’ve seen, this isn’t the case for most people. Cancer mostly occurs in older people. It is a common disease. 1 in 3 people in the UK get cancer at some point in their lives. So, most families will include at least one person who has had cancer. Having a couple of relatives diagnosed with cancer when over the age of 60 doesn’t mean there is a cancer gene running in the family.

Genetics specialists estimate that only about 2 or 3 in every 100 cancers diagnosed (2 – 3%) are linked to an inherited gene fault.

The strength of your family history depends on

  • Who in your family has had cancer
  • How old they were at diagnosis

The more relatives who have had the same or related cancers, and the younger they were at diagnosis, the stronger your family history. And the more likely it is that cancers are being caused by an inherited faulty gene. You may have a strong family history if any of these situations apply to you

  • More than 2 close relatives on the same side of your family have had cancer (the same side of your family means either your father’s relatives or your mother’s relatives)
  • They have had the same type of cancer, or different cancers that can be caused by the same gene fault
  • The cancers developed when they were young, below the age of 50
  • One of your relatives has had a gene fault found by genetic tests

Remember - cancer is most common in people over the age of 60 and is rare in young people. So cancer in older people is less likely to be due to an inherited cancer gene.

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Updated: 15 August 2013