Predictive genetic tests for cancer risk genes
Cancer is not usually inherited, but some types – mainly breast, ovarian, colorectal and prostate cancer – can be strongly influenced by genes and can run in families.
We all carry certain genes that are normally protective against cancer. These genes correct any DNA damage that naturally happens when cells divide.
Inheriting faulty versions or "variants" of these genes significantly raises your risk of developing cancer, because the altered genes cannot repair the damaged cells, which can build up and form a tumour.
BRCA1 and BRCA2 are examples of genes that raise your cancer risk if they become altered. Having a variant BRCA gene greatly increases a woman's chance of developing breast cancer and ovarian cancer. They also increase a man's chance of developing male breast cancer and prostate cancer.
BRCA genes are not the only cancer risk genes. Researchers recently identified more than 100 new gene variants associated with an increased risk of breast, prostate and ovarian cancer. Individually, these new gene variants only slightly increase the risk of cancer, but a combination could mean a high risk overall.
If you or your partner have a high-risk cancer gene, such as an altered version of BRCA1, it can be passed on to any children you have.
What to do if you're worried
Speak to a GP if cancer runs in your family and you're worried you may get it too. They may refer you to a local genetics service for an NHS genetic test, which will tell you if you have inherited one of the cancer risk genes.
This type of testing is known as predictive genetic testing. It's "predictive" because a positive result means you have a greatly increased risk of developing cancer. It does not mean you have cancer or are definitely going to develop it.
You may be eligible for this NHS test if the faulty gene has already been identified in one of your relatives, or if there is a strong family history of cancer in your family.
Pros and cons of having a predictive genetic test
Not everyone who is eligible for the NHS test will want to have it. It's a personal decision, and should only be made after you've had genetic counselling and talked through what having the test means, how you may feel and how you will cope.
A positive result means you can take steps to manage your risk of developing cancer.
You can make certain lifestyle changes to lower your risk, have regular screening and have preventative treatment.
Knowing the result may reduce any stress and anxiety that comes from not knowing.
The results of some genetic tests are inconclusive. This means doctors may identify a variation in a gene, but not know what effect it may have.
A positive result may cause permanent anxiety. Some people would rather not know about their risk and only want to be told if they actually develop cancer.
What testing involves
There are usually 2 steps to genetic testing:
- A relative with cancer has a diagnostic blood test to see if they have a cancer risk gene (this must happen before any healthy relatives are tested). Their result will be ready 6 to 8 weeks later.
- If your relative's test is positive, you can have the predictive genetic test to see if you have the same faulty gene. Your GP will refer you to a local genetics service for a blood test (you'll need a copy of your relative's test results). The result will usually take up to 2 - 4 weeks to come through after a blood sample is taken, but this may not happen at your first appointment. This test is very likely to find the faulty gene but on rare occasions it may miss it.
When there are no affected relatives available, full testing of BRCA1 and BRCA2 may be possible for those with at least a 10% chance of having a faulty gene. This usually means having a very strong family history of early onset breast and particularly ovarian cancer. It can take 4 to 8 weeks or longer to get the result.
What a positive result means
If your predictive genetic test result is positive, it means you have a faulty gene that raises your risk of developing cancer.
It does not mean you are guaranteed to get cancer – your genes only partly influence your future health risks. Other factors, such as your medical history, lifestyle and your environment, also play a role.
If you have one of the faulty BRCA genes, there is a 50% chance you will pass this on to any children you have and a 50% chance that each of your siblings also has it.
You may want to discuss your results with other members of your family, who may also be affected. Staff at the genetics clinic will discuss with you how a positive or negative result will affect your life and your relationships with your family.
You can read more about BRCA1 and BRCA2 in the beginner's guide to BRCA1 and BRCA2 (PDF, 866kb) produced by The Royal Marsden NHS Foundation Trust.
Insurance companies cannot ask you to disclose the results of predictive genetic tests for the majority of policies, but this may change in the future.
Managing your risk
If your test result is positive, you have a range of options to manage your risk. Risk-reducing surgery is not the only option.
Ultimately, there's no right or wrong answer about what you should do – it's a decision only you can make.
Regularly examining your breasts
If you have the faulty BRCA1/2 gene, it's a good idea to be aware of changes in your breasts. Find out more about being breast cancer aware.
This advice applies to men with a faulty BRCA2 gene too, as they are also at increased risk of breast cancer (although to a lesser extent).
Detecting breast cancer at an early stage means it may be easier to treat. The chance of making a full recovery from breast cancer, especially if it is detected early, is relatively high compared with other forms of cancer.
Unfortunately, there's currently no reliable screening test for ovarian cancer or prostate cancer. Read more about screening for prostate cancer. However, annual PSA tests for prostate cancer may benefit men who carry the faulty BRCA2 gene.
Changes in your lifestyle can sometimes reduce your individual cancer risk. These include taking plenty of exercise and eating a healthy diet.
If you have a faulty BRCA gene, be aware of other factors that could increase your risk of breast cancer. It's recommended that you avoid:
- the oral contraceptive pill
- drinking more than the maximum recommended daily limits of alcohol
- being overweight
The National Institute for Health and Care Excellence (NICE) also recommends that women with a family history of breast cancer breastfeed their children, if possible.
Find out more about things that may help to prevent ovarian cancer.
NICE recommends medicines called tamoxifen, raloxifene and anastrozole for some women who are at an increased risk of breast cancer.
These can reduce your risk of getting breast cancer for many years.
Find out more about medicine to prevent breast cancer.
Risk-reducing surgery means removing all the tissue (such as the breasts or ovaries) that could become cancerous. Carriers of a faulty BRCA gene may wish to consider a preventative mastectomy.
Women who have risk-reducing mastectomies reduce their risk of developing breast cancer by around 50%. However, a mastectomy is a major operation and recovering from it can be physically and emotionally difficult.
Surgery can also be used to reduce ovarian cancer risk. Women who have their ovaries removed before the menopause not only dramatically reduce their chances of developing ovarian cancer, but also reduce their chances of developing breast cancer by up to 50%.
However, this will trigger early menopause and mean you're not able to have your own children (unless you store eggs or embryos).
If you have not had breast cancer, you’ll be offered hormone replacement therapy (HRT) until you’re about 50 years old. This is to protect against heart disease and thinning of your bones. If you have had breast cancer, you will not be offered HRT.
Read more about surgery to remove the ovaries, including the risks and after-effects.
The risk of ovarian cancer in women who carry a BRCA gene fault does not begin to rise significantly until about the age of 40. Therefore, carriers of the faulty gene who are younger than 40 usually wait to have this operation.
Telling close relatives
Your genetics unit will not approach your relatives about your result – it will usually be up to you to tell your family.
You may be given a standard letter to share with relatives, which explains your test result and contains all the information they need to be referred for the test themselves.
However, not everyone will want to have the genetic test. Women who are closely related to you (such as your sister or daughter) can have cancer screening without having genetic testing.
Planning a family
Cancer risk genes can be passed on to any children you have. If your predictive genetic test is positive and you want to start a family, you have several options. You can:
- have your children without any intervention, and risk your child inheriting the faulty gene
- adopt a baby
- use donor eggs or donor sperm (depending on who carries the faulty gene) to avoid passing on the faulty gene
- discuss prenatal testing with your doctor – but testing an unborn baby for genes that may cause cancer in later life, using CVS or amniocentesis, is not routinely offered
- have pre-implantation genetic diagnosis – a technique used to select embryos that have not inherited the faulty gene; but there's no guarantee this technique will result in a successful pregnancy, and NHS funding for it may not be available to all patients
Paying for private testing
If there is not a strong family history of cancer in your family and the faulty gene has not otherwise been identified in any of your relatives, you will not be eligible for the NHS genetic test.
You'll have to pay for it privately if you still wish to have the test. Consider this carefully, because:
- if you do not have any family history of cancer, it's less likely you have one of the faulty genes
- the tests can be expensive, potentially costing around £1,000 or more
- there's no guarantee they will predict whether you'll develop cancer
- you may not be offered genetic counselling to help you make a decision and support you once you get your results
About BRCA1 and BRCA2
Women with the faulty BRCA1 gene, for example, have a 65 to 79% lifetime risk of breast cancer and a 36 to 53% risk of ovarian cancer before the age of 80. In other words, out of every 100 women with the faulty BRCA1 gene, between 65 and 79 will develop breast cancer in their lifetime and between 36 and 53 will develop ovarian cancer.
The faulty BRCA genes affect around 1 in every 300 to 400 people, but people of Ashkenazi Jewish descent are at a much higher risk (as many as 1 in 40 may carry the faulty gene).
Page last reviewed: 8 July 2021
Next review due: 8 July 2024