Genetic testing

Genetic testing looks for gene mutations that may increase the risk of cancer in a family.

Your genetics specialist will explain if testing is possible for you. Before you have testing, you may want to discuss the possible advantages and disadvantages.

Testing is usually done in 2 stages. A blood sample from a family member who has had cancer is tested. If a cancer gene mutation is found, other family members are tested for the same mutation.

The test results may be one of the following:

  • The test finds a cancer gene mutation – This means you have an increased risk of some cancer types. You will get advice about managing this risk. Other family members may also have the mutation.
  • The test does not find a cancer gene mutation – This may mean there is no mutation. It can also mean there is an unidentified mutation or several ‘low-risk’ mutations.
  • The test finds a mutation that has not been clearly linked to cancer.

Tests do not always give clear answers. Your specialist will explain your results and give you support.

What is genetic testing?

Genetic testing can be used to look for inherited gene mutations that raise the risk of cancer in a family. Tests may be possible and useful if:

  • you are diagnosed with a cancer that is likely to be linked to an inherited mutation
  • a close blood relative has already had a test that found an inherited cancer gene.

Genetic testing – a 2-step process

There are usually 2 steps to genetic testing.

Step 1 – Mutation search

This is also called diagnostic testing. First, the laboratory looks for the gene mutation that may run in your family. They do this on a blood sample from someone in your family who has had cancer. It usually takes up to about 8 weeks to get the results.

The test may:

  • find a cancer gene mutation
  • not find a cancer gene mutation
  • find a variant of uncertain significance (see below).

Step 2 – Predictive testing

If the mutation search finds a cancer gene mutation, other family members can then be tested for the same mutation.

A predictive test is faster than a mutation search. This is because the laboratory knows which gene change to look for and where to find it.

If there is no living relative with cancer

Usually, a person in the family who has had cancer is tested first. If a cancer gene mutation is found, other members of the family can have predictive testing.

But sometimes there is no living relative with cancer who can be tested first. You may still be offered a genetic test if:

  • the pattern of cancer in your family strongly suggests there could be a gene mutation
  • you have a family history of cancer and you are from an Eastern European or Ashkenazi Jewish (Eastern European Jewish) background – some inherited cancer genes are more common in these ethnic groups.

Genetic testing in children

Most inherited cancer genes do not cause cancers in children. Because of this, children are not usually tested. Once they become adults, they can make their own decisions about testing.

A child may be tested if there is a chance they have a gene mutation that causes health problems before adulthood. For example, a condition called familial adenomatous polyposis (FAP) causes growths in the bowel (polyps). These usually start to appear when a person is in their teens. Unless the polyps are treated, they will eventually develop into bowel cancer. It is useful to know if a child carries the gene mutation that causes FAP, so they can have regular tests to monitor the bowel from their early teens.

Other rarer conditions where children are tested for inherited gene mutations include:

  • the multiple endocrine neoplasia (MEN) syndromes MEN1 and MEN2
  • Von Hippel-Lindau syndrome (VHL)
  • Li-Fraumeni syndrome.

Children affected by these conditions have a higher risk of cancer and other health problems before they are adults.

Before having genetic testing

Your genetics specialist will explain what to expect. There may be several things to think about before you decide to have a genetic test.

Possible advantages

  • The test may show you do not have the gene mutation and that your cancer risk is low. You will not need to consider extra screening or risk-reducing treatments. You will know you cannot pass on the cancer gene to any children you have.
  • If you find out you have a gene mutation, this may help you decide how to reduce your cancer risk. Your options may include having screening to find a cancer early, making lifestyle changes and having treatments to reduce your risk of getting cancer.

Possible disadvantages

  • If you find out you have a gene mutation, you may feel more worried about getting cancer.
  • Tests do not always give clear answers. Some people find out they have a change in a gene, but it is not known how this affects their cancer risk. Doctors call this a variant of uncertain significance (see below).
  • You may be told you have a raised cancer risk, even if testing does not find a gene mutation. This is because your family history may still show that an unknown gene mutation is likely.
  • If you find out you have a gene mutation, you will need to decide whether or how to tell relatives (see below). Many people find this difficult.

I was surprised by how much counselling there is before the test. You can talk to a counsellor as much as you want, to make sure you want the test.



Some people worry insurance companies will refuse to insure them or will charge more if they have a genetic test. There is no law to prevent this. But for now, the Association of British Insurers (ABI) and the government have agreed how an insurer can use the results of genetic testing. This is called the Concordat and Moratorium on Genetics and Insurance.

The agreement lasts until 2019. It may change after that. It only covers genetic testing. It is not about your personal or family history of cancer. Insurance companies may still ask questions about your and your family’s health, and any cancer diagnoses.

The agreement says that an insurer will not ask you to take a genetic test. Sometimes they will ask for the results of genetic testing you have already had. If you do not have cancer, they will not ask for results of genetic tests for inherited cancer genes.

You can find more information from:


Your doctor and genetic specialist cannot tell anyone you have had a genetic test, or the result, unless you agree to this.

When they take your blood for the genetic test, they may ask if they can also take a sample for research. This may help scientists to find other cancer genes in the future. The research scientists will not know your personal details.

If you are worried about your personal details and confidentiality, talk to your doctor or nurse. They will explain how your information is used and protected.

I gave consent for my sample to be kept and tested if future tests become available. This also means they can do research to find out what works for people.


If a cancer gene is found

This means you have inherited a gene mutation that increases your risk of getting some cancer types.

Other members of your family

If you have an inherited cancer gene, this may affect other people in your family. You may have to decide if and how to tell them.

Your genetics specialist may give you a letter you can give to family members. It will help explain your results and what it may mean for them. They can then decide whether they also want to have genetic counselling and predictive testing. Their GP can refer them to their nearest genetics clinic or family cancer centre.

Some people in your family may find they have the same gene mutation and an increased risk of getting cancer. Others may find they have not inherited it. They still have the same risk of getting cancer as people in general, but they will not need extra screening or risk-reducing treatments. They should still consider taking part in NHS screening when they are sent an invitation. They should also follow a healthy lifestyle.

Your feelings

Talking about an inherited cancer gene with your family can be difficult. People may have questions that you cannot answer or have feelings you did not expect.

It is important to remember that no one is to blame for the genes they inherit or pass on. People with a gene mutation sometimes have feelings of guilt, blame or responsibility. But we cannot control the genes we pass on.

If there are children in your family, we have more information about talking to children about an inherited cancer gene that you may find helpful.

Your genetics specialist can help you talk through your feelings. Some organisations can offer support. You can also talk to our cancer support specialists on 0808 808 00 00 (Monday to Friday, 9am to 8pm).

Since my diagnosis as a carrier of the HNPCC gene, my uncle tested negative. His side of the family have no greater chance of developing bowel cancer than the general public.


If the mutation search does not find a cancer gene

The mutation search may not find a cancer gene. This can happen even if you have a strong family history of cancer. It may be that:

  • there is a gene mutation in the family, but it is not one we currently know about or test for routinely
  • there are several ‘lower-risk’ genes in the family – these, together with environmental factors, can still increase the risk of cancer
  • the cancers in the family are not due to an inherited cancer gene – the cancers may have happened by chance or for other reasons we do not understand.

Your feelings

You may have mixed feelings if you are told the test has not found a gene mutation.

You may feel relieved that an inherited cancer gene has not been found. But this result also means you cannot know for certain if cancer is an inherited problem in your family.

Your genetics specialist may explain that you still have a higher risk of cancer based on your family history. This means the pattern of cancer in your family is unusual and may be caused by an unknown gene mutation. You may be offered extra screening or risk-reducing treatments. Because you have less clear information about your risk, it may be more difficult to decide what you want to do.

You may decide to reduce your cancer risk and improve your health in other ways. This may include giving up smoking, eating a healthy diet and being more physically active.

Variants of uncertain significance (VUS)

Sometimes the mutation search finds a gene mutation that has not been clearly linked to cancer. Doctors call this a variant of uncertain significance. This means it is not clear whether the gene mutation is the cause of the cancer.

Because of this, the genetics specialist cannot offer predictive testing to other people in the family. They may ask for blood samples from them to try to get more information. These extra tests may help them decide if the gene mutation is the reason for the pattern of cancer in the family.

The family may also be asked to keep in contact with the genetics clinic. This is in case they find out more about the gene in future.

Back to Family history and genetics

Cancer and genes

Gene changes (mutations) in a cell may mean the cell stops working normally. This can eventually cause cancer to develop.