Genetic testing for cancer

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.

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).

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.

• 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.

• 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.

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.

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.

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.

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:

• GOV.UK – the Code on Genetic Testing and Insurance
• the Association of British Insurers (ABI)
• your genetics specialist.
• the Genetic Alliance