Genetic testing

Genetic testing is usually offered to the person in your family with cancer. If a cancer gene is found, other family members can choose to be tested. Children aren’t usually tested.

Genetic testing is done in two stages:

  • Step 1 Mutation search – The laboratory look for the cancer gene using a blood sample from the person who has cancer.
  • Step 2 Predictive testing – If a mutation is found at stage 1, other family members will be tested.

If a cancer gene mutation is found, this means you have an increased risk of getting a specific cancer. You might want to tell other family members so they can get tested. Having a faulty gene isn’t your fault and there is lots of support available for you and your family.

If a cancer gene mutation isn’t found, this is called no mutation detected (NMD). This can happen even if there is a strong family history.

Sometimes testing finds a mutated gene that has not been clearly linked with cancer risk. This is called a variant of uncertain significance. Because it’s unclear whether the mutation caused the cancers in your family, predictive testing isn’t offered. 

Who is offered genetic testing?

Usually a person in the family who has had cancer has the test first. If a cancer gene is found, other members of the family can choose to have a test.

Sometimes, no living relative with cancer can be tested. In this case you may be offered a genetic test. But only if your family history strongly suggests there could be a cancer gene in your family.

If you have a family history of cancer, and have Ashkenazi Jewish or Polish ancestry, you may also be able to have a genetic test without a relative who has had cancer being tested first.

Genetic testing in children

Most cancer genes don’t cause cancers in children. Because of this children aren’t usually tested. Once they become adults they can make their own decisions about testing.

There are some exceptions to this. The main one is familial adenomatous polyposis (FAP). The FAP gene can cause growths in the bowel (polyps) from the age of 13. Because of this, young people with FAP usually have bowel screening from the age of 12.

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

  • Multiple endocrine neoplasia type 2 (MEN2) which can cause medullary thyroid cancer in young children.
  • Von Hippel-Lindau (VHL) which can cause non-cancerous growths in the body in childhood as well as cancer in the kidney in young adults.
  • Li Fraumeni syndrome which increases the risk of cancer in childhood.

We have more information about MEN2.

Genetic testing – a two-step process

Genetic testing is usually done in two stages. These are the mutation search and predictive testing.

Step 1 – mutation search

First, the laboratory looks for the cancer gene that may run in your family. They do this on a blood sample from a member of your family who has had cancer. Doctors call this the mutation search. It usually takes up to about eight weeks for the results to be available.

Results of a mutation search may:

  • find a cancer gene mutation
  • not find a cancer gene mutation
  • find a gene mutation that isn’t known to cause cancer.

Step 2 – predictive testing

If the mutation search finds a cancer gene mutation, you and other family members can have a genetic test. Doctors call this predictive testing.

Predictive testing is faster than mutation searching. This is because the laboratory knows which gene change to look for and where to find it.

If a cancer gene mutation is found

This means you have inherited a cancer gene. This gene increases your risk of getting a specific cancer. Doctors sometimes call this a positive test result.

Other members of the family

If you have an inherited cancer gene, you may wish to tell family members so they can decide whether to have genetic counselling and predictive testing. This can identify who in your family has an increased risk of getting cancer and who doesn’t.

Medical test results are always confidential. Because of this, no one but you can tell relatives about your results.

Your genetics specialist may give you a letter you can give to family members. It will help explain the results and what it may mean for them. Their GP can refer them to their nearest genetics clinic or family cancer centre.

Family members who find they have not inherited the gene mutation in the family have a much lower risk of getting cancer. But it doesn’t mean they definitely won’t get cancer. They still have the same risk of getting cancer as people in general.

They won’t need extra screening or risk-reducing treatments. But they should still consider taking part in national screening programmes for the general population when invited to do so.

Your feelings

Talking about a cancer gene in the family can be difficult. People often worry about when and what to tell their children if they find out they have an inherited cancer gene. 

It’s important to remember that having a cancer gene mutation isn’t your fault. No one is to blame for the genes they inherit or pass on.

Families sometimes have feelings of guilt, blame or responsibility. But, the genes we inherit and pass on is down to chance. We are no more responsible for inheriting a cancer gene than we are for our eye colour.

Your genetics specialist can help you talk through your feelings. You can call our cancer support specialists on 0808 808 00 00.

I have been to see a genetics consultant and he recommended that my daughters be screened from their late 20s, which I am happy with.


If a cancer gene mutation is not found

If the mutation search does not find a cancer gene mutation, doctors call this no mutation detected or NMD.

Genetic testing does not always find a cancer gene in the family even if there is a strong family history.

There are several possible reasons for a test not showing a gene mutation:

  • There is a gene mutation in the family but it is in a gene that doctors have not yet identified.
  • There are several ‘low-risk’ genes in the family. These, in combination 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 have happened by chance or for other reasons we don’t understand.

Your feelings

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

You may feel relieved that a gene mutation, which greatly increases the risk of cancer, hasn’t been found. But this result also means that you can’t know for certain if cancer is an inherited problem in your family. And it’s not possible for you to find out your individual risk of cancer.

Your doctor and genetics specialist may still consider you at increased risk of cancer based on your family history. There are ways of managing a high risk of cancer. You may be offered screening and some people are also offered risk-reducing treatments. But deciding about having risk-reducing treatment can be more difficult when you don’t have definite information about your risk.

You may decide to make certain changes to your lifestyle to improve your general health. This may include giving up smoking, eating a healthy diet and being more physically active.

If the result is uncertain

Sometimes a genetic test finds a mutation in a gene. But the mutation has not been clearly linked with increased cancer risk. Doctors call this a variant of uncertain significance (VUS).This means it is unclear whether the gene mutation is the cause of the cancers in your family.

Because of this, the genetics specialist cannot offer predictive testing to other people in your family. But they may ask for samples from them to try to get more information. These extra tests may help them to decide if the gene mutation (VUS) is the reason for a family history of cancer.

You may also be asked to keep in contact with the genetics clinic. This is in case they discover more about the particular mutation found in your gene in future.

Genetic testing and risk-reducing surgery for breast cancer

Wendy and her daughter Becky share their experiences of genetic counselling and genetic testing.

About our cancer information videos

Genetic testing and risk-reducing surgery for breast cancer

Wendy and her daughter Becky share their experiences of genetic counselling and genetic testing.

About our cancer information videos