Cancer and genes

Your body is made up of tiny building blocks called cells. Inside every cell is a set of genes that tell the cell what to do.

Sometimes a gene is changed and cannot give the correct instructions. This change is called a gene mutation. Eventually, mutations in a cell may mean the cell stops working normally. Cancer develops when cells like this multiply in an abnormal way.

Most cancers are caused by mutations that happen during a person’s lifetime (acquired mutations). Acquired mutations happen in a cell by chance or may be caused by your lifestyle or environment.

An inherited mutation is a gene change that has passed from 1 of your parents to you. Most cases of cancer are not caused by inherited mutations. But some inherited mutations can make cancer more likely to develop. You won’t definitely get cancer if you have this type of mutation. You may have a higher risk of developing cancer. There may also be several people in your family who have the same types of cancer, or were younger than usual when diagnosed.

How do genes work?

Your body is made up of tiny building blocks called cells. Inside every cell is a set of genes. They are the instructions the cell needs to work properly. Genes control:

  • how a cell does its job in the body
  • when it divides to make new cells
  • the cell’s death when it is not needed any more.

Sometimes the structure inside a gene is permanently changed, so the gene no longer gives the correct instructions. This change is called a gene mutation.

Some cells in your body develop gene mutations during your lifetime. These are called acquired mutations. It is also possible to have a gene mutation because it passed from one of your parents to you. This is called an inherited mutation.

Eventually, gene mutations in a cell may mean the cell stops working normally. Cancer develops when cells like this can multiply in an abnormal way and grow out of control.

Cells forming a tumour
Cells forming a tumour

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What is an acquired mutation?

Most cancers are caused by acquired mutations. These are gene changes that happen in a person’s cells during their lifetime.

A cancer may develop because of acquired mutations in cells in a certain part of the body. For example, if genes in cells in the lungs are damaged, lung cancer may eventually develop.

Acquired mutations may happen:

  • by chance, as a cell divides or does its job in the body
  • because of your lifestyle (for example, your diet or physical activity levels)
  • because of things in your environment (such as sunlight or tobacco smoke).

Your cells can repair a lot of this damage. But over time, enough damage may build up in a cell to allow cancer to develop. This can take many years, which is why cancer is more common in older people.

Remember, this type of mutation only affects genes in some cells. It rarely affects genes in sperm or egg cells. This means acquired mutations cannot be passed on to children.


What is an inherited mutation?

Genes are passed from parent to child (inherited) when a sperm and egg join to start a pregnancy (conception). We have two copies of each gene – one from our mother and the other from our father. The sperm contains one copy of the father’s genes. The egg contains one copy of the mother’s genes. If one of the sets of genes contains a mutation, the child will have this mutation in their cells.

Some inherited mutations make a person more likely to develop certain types of cancer. If you inherit a gene mutation like this, it does not mean you have cancer. More damage (acquired mutations) still needs to happen before a cancer can develop. The inherited gene mutation may allow this damage to build up faster.

Usually, the risk of cancer is only higher once you are an adult. Only a few inherited mutations increase the risk of cancer in children.

You might hear different names for the inherited mutations that make cancer more likely. These include:

  • inherited cancer genes
  • cancer predisposition genes
  • cancer susceptibility genes.

What are the chances of inheriting a gene mutation?

You only get one copy of each of your parent’s genes. If one parent has a gene mutation, you either will get the copy containing the mutation, or you will not. There is a 1 in 2 (50%) chance the mutation is passed on.

How genes are passed on
How genes are passed on

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If you have the gene mutation, there is a 1 in 2 (50%) chance any children you have will inherit it.


Inherited cancer genes

Scientists have found many of the inherited mutations that are linked to common cancers, such as breast, bowel, ovarian and womb cancer. There are likely to be other inherited mutations that have not been found yet for these and other types of cancer.

If a family is affected by a gene mutation, there may be a pattern of cancers diagnosed in that family. There may be several people who:

  • have the same types of cancer
  • were younger than usual when they were diagnosed.


When cancers happen together

A mutation in one gene may be linked to several types of cancer. This means a family with one inherited mutation may be affected by a group of cancers.

The most common patterns where cancers happen together are:

  • breast and ovarian cancer
  • bowel and womb cancer (sometimes with cancers of the ovary, stomach or kidney).

Less often, other patterns of cancers are seen in a family. We have more information about other inherited cancers.


Lower-risk genes

Some inherited cancer genes cause a high risk of cancer. Scientists have also found other gene mutations that slightly increase the risk of cancer. These are sometimes called low-penetrance genes. The effect of each mutation on its own is small. But if a person has several of these mutations, they may still have a high risk of certain cancers. These genes are not yet routinely tested for.

There are probably many lower-risk genes we do not know about yet. Researchers are trying to find out more about these genes and how they interact with other risk factors to cause cancer to develop.


Can cancer genes ‘skip’ a generation?

Cancer genes cannot ‘skip’ or miss a generation. If one of your parents has a gene mutation, there is a 1 in 2 (50%) chance it has been passed on to you. So either you inherit it or you do not. If you do not inherit the mutation, you cannot pass it on to your children.

Sometimes it can seem like the cancer skipped a generation. This is usually because a person in the family has the mutation and passes it to their child. But they do not develop cancer themselves.

Gene mutations linked to breast and ovarian cancers can pass through the father’s side of the family. A man who inherits this type of mutation is unlikely to develop breast cancer and cannot develop ovarian cancer. But he still has a 50% chance of passing it on to his children.

If his daughter inherits the mutation from him and develops breast cancer, it can look like the cancer gene has skipped a generation.


How often is cancer caused by inherited cancer genes?

Most cases of cancer are not caused by an inherited mutation. Only a small number of people get cancer that is clearly linked to an inherited cancer gene. Experts think that less than 5 in 100 (5%) of all cancer cases are caused by an inherited cancer gene.

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Genetic testing

You will only be offered genetic testing if your family history suggests you may have inherited a cancer gene.