Genetic testing for inherited cancer genes

Genetic testing can be used to look for gene variants that increase the risk of cancer in a family. A genetics specialist can tell you whether a test may be possible and useful in your situation.

For example, you may be offered genetic testing if you have a:

  • close blood relative who had a genetic test that found an inherited cancer gene variant
  • cancer that is likely to be linked to a gene variant.

The results of genetic testing may affect other people in your family.

Other types of cancer genetic tests

The information on this page is about genetic testing when cancer may run in a family.

A different type of test may be used to look at the genes in a sample of cancer cells. When you are diagnosed with a cancer, your doctor may suggest this type of test. It looks for gene changes that affect the cancer cells (acquired variants). It does not look for gene variants that can pass from a parent to a child (inherited variants).

Your cancer doctor can give you more information. We also discuss this in our information about personalised medicine.

How is genetic testing done?

There are 2 steps to genetic testing for an inherited cancer gene variant.

Step 1 - Usually, a person in the family who has had cancer is tested first. This is called diagnostic testing.

Step 2 - If a cancer gene variant is found, other members of the family can be tested for the same variant. This is called predictive testing.

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 a gene variant. This is called an indirect genetic test.

What is diagnostic testing?

First, the laboratory looks for the gene variant 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 variant
  • not find a cancer gene variant
  • find a variant of uncertain significance (see below).

What is predictive testing?

If diagnostic testing finds a cancer gene variant, other family members can be tested for the same variant. This is called predictive testing or pre-symptomatic testing.

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

Genetic testing in children

Most inherited cancer genes do not cause cancers in childhood. This means children are not usually tested. When they become adults, they can make their own decisions about testing.

A child may be tested if they might have inherited a gene variant that causes health problems before adulthood. For example, a variant in the APC gene can cause a condition called familial adenomatous polyposis (FAP). FAP causes a high risk of bowel cancer. People affected by FAP may need to start treatment to prevent bowel cancer when they are in their teens. 

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

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

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 benefits

  • Predictive genetic testing may show you do not have a gene variant carried by someone else in your family. This means that your cancer risk is the same as anyone in the general population. You will not need to consider extra screening or risk-reducing treatments. You will know you cannot pass the gene variant to any children you have.
  • If you find out you have a gene variant, this may help you decide how to reduce your cancer risk. Your options may include screening to find a cancer early, risk-reducing treatments and lifestyle changes.

Possible disadvantages

  • If you find out you have a gene variant, you may feel more worried about getting cancer.
  • Diagnostic genetic testing does 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).
  • Even if diagnostic genetic testing does not find a gene variant, you may be told you have a raised cancer risk. This is because your family history may show that there could be an unknown gene variant. Or there could be a combination of lower-risk inherited gene variants that increase your cancer risk.
  • If you find out you have a gene variant, you will need to decide whether or how to tell other family members that may be affected.

Your test results

Your genetics specialist will tell you when you are likely to get your test results. You may feel anxious about getting your results. It can help to have someone with you for support and to help you to remember what was said.

If a cancer gene variant is found

This means you have a gene variant that increases your risk of getting some cancer types. Your genetics specialist will give you more information about:

  • your level of risk
  • the types of cancer you are at risk of getting
  • ways of managing the risk.

This can be a lot to understand and think about. Your genetics specialist may give you information to read. They will support you and answer any questions you have.

Other members of your family

If you have a cancer gene variant, this may affect other people in your family. You may have to decide whether and how to tell them.

Talking about this with your family can be difficult. People may have questions that you cannot answer. They may have feelings you did not expect.

It is important to remember that nobody is to blame for the genes they inherit or pass on. People with a gene variant sometimes have feelings of guilt, blame or responsibility. But nobody can control the genes they inherit or pass on.

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.

If there are children in your family, your genetics specialist can explain what your test results may mean for them at different ages. The genetics specialist can support you with more information about talking to children and teenagers about your test results.

If a cancer gene variant is not found

Genetic testing may not find a cancer gene. This can mean different things depending on the stage of genetic testing.

No cancer gene variant is found during diagnostic testing

This can happen even if you have a strong family history of cancer. It may be one of the following:

  • The cancers in the family are not due to an inherited gene variant. They may have happened by chance or for other reasons doctors do not understand.
  • There is a gene variant in the family, but it is not one doctors know about or usually test for.
  • There are several lower-risk gene variants in the family. These are not usually tested for, but they can increase the risk of cancer when combined with environmental factors.

You may feel relieved an inherited cancer gene has not been found. But you may not know for certain whether 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 variant.

It can be hard coping with uncertainly about the future. It may help to talk about your feelings with your family, friends, GP or genetics specialist. You can also call the Macmillan Support Line for free on 0808 800 00 00.

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 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.

You can find out more about managing hereditary cancer risk on our page about family history, genes and cancer risk.

No cancer gene variant is found during predictive testing

Predictive testing only looks for a cancer gene variant that is known to run in your family. If the test does not find that cancer gene variant, your cancer risk is the same as anyone in the general population. You will not need extra screening or risk-reducing treatments. You cannot pass that gene variant to any children you have.

You may feel relieved that you are not affected by the cancer gene variant that affects your family. But other family members may be affected, and you may feel guilty or worried for them.

Variants of uncertain significance (VUS)

Sometimes diagnostic testing finds a gene variant 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 variant 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 whether the pattern of cancer in the family is due to the gene variant.

The family may also be asked to keep in contact with the genetics clinic. This is in case more information becomes available about the gene variant. The variant may be found to be the cause of the cancer in the family. Or it may be found to be harmless.

Confidentiality and genetic testing

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

When they take your blood for the genetic test, they may ask whether they can also take a sample for research. This may help researchers find other cancer gene variants in the future. Researchers are not given your personal details.

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

Insurance and genetic testing

Some people worry insurance companies will refuse to insure them or will charge more if they have genetic testing for cancer. There is no law to prevent insurance companies from doing this. But some insurance companies have signed up to the Code on Genetic Testing and Insurance. This means they will not:

  • ask you to have a predictive or diagnostic genetic test
  • ask for, or use the result of, a predictive genetic test if you are applying for insurance.

Insurance companies may still ask about your health, your family’s health, and whether anybody in your family has had cancer. They may ask for the results of diagnostic testing if you have already had this.

You can find more information from:

About our information

  • References

    Below is a sample of the sources used in our family history and cancer information. If you would like more information about the sources we use, please contact us at

    Monahan KJ, Bradshaw N, Dolwani S, et al. Guidelines for the management of hereditary colorectal cancer from the British Society of Gastroenterology (BSG)/Association of Coloproctology of Great Britain and Ireland (ACPGBI)/United Kingdom Cancer Genetics Group (UKCGG). Gut. 2020; 69: 411–444. Available from DOI: 10.1136/gutjnl-2019-319915 (accessed October 2022).

    NICE. Familial breast cancer: classification, care and managing breast cancer and related risks in people with a family history of breast cancer. Clinical guideline [CG164]. Last updated: 20 November 2019. Available from (accessed October 2022).

    NICE. Molecular testing strategies for Lynch syndrome in people with colorectal cancer. Diagnostics guidance [DG27]. Published: 22 February 2017. Available from (accessed October 2022).

    NICE. Testing strategies for Lynch syndrome in people with endometrial cancer. Diagnostics guidance [DG42]. Published: 28 October 2020. Available from (accessed October 2022).

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Marc Tischkowitz, Reader and Honorary Consultant Physician in Medical Genetics.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 October 2022
Next review: 01 October 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.