Predictive genetic tests for cancer risk genesOverview
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 – they correct any DNA damage that naturally occurs 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 two 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. This was the reason Angelina Jolie had preventative breast cancer surgery, followed by ovarian cancer surgery. 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.
If you're concerned, read on.
What to do if you're worried
Speak to your 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 doesn't 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. See What testing involves, below.
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 sessions 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 (see Managing your risk, below)
- knowing the result may reduce any stress and anxiety that comes from not knowing
- the results of some genetic tests are inconclusive – 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 normally happen before any healthy relatives are tested). Their result will be ready 4 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 your local genetics service for the blood test (you'll need a copy of your relative's test results). The result will take up to 2 weeks to come through after a blood sample is taken, but this may not happen at your first appointment. This test is fully predictive as a "clear" negative test, which will mean you have not inherited the family high risk of cancer.
The charity Breakthrough Breast Cancer explains the importance of these 2 steps:
"Without looking at the genes of an affected relative first, testing a healthy individual would be like reading through an entire book looking for a spelling mistake without knowing where the mistake is, or if there is a mistake at all."
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 genetic fault. This usually means having a very strong family history of early onset breast and particularly ovarian cancer. It takes 4 to 8 weeks to get the result, but this is not fully predictive as a negative test, so cannot rule out that the problem in relatives is due to a different gene.
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 doesn't 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. 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 this 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. Read 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 if you are over 35
- combined hormone replacement therapy (HRT) if you’re over 50
- 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.
Read about the 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.
Read about medication 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 90%. 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 risk of developing ovarian cancer, but also reduce their risk of developing breast cancer by up to 50%. However, this will trigger an early menopause and mean you're not able to have your own children (unless you store eggs or embryos). 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.
- Have prenatal testing, which is a test done in pregnancy that reveals whether your baby has the faulty gene. You can then plan to continue or terminate the pregnancy, depending on the test result.
- Have pre-implantation genetic diagnosis – a technique used to select embryos that have not inherited the faulty gene. However, there is no guarantee this technique will result in a successful pregnancy, and funding for it on the NHS may not be available to all patients.
Paying for private testing
If there isn't a strong family history of cancer in your family and the faulty gene hasn't otherwise been identified in any of your relatives, you won't 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 don't have any family history of cancer, it's unlikely you have one of the faulty genes
- the tests can be expensive, potentially costing up to £500 to £2,000 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 60 to 90% lifetime risk of breast cancer and a 40 to 60% risk of ovarian cancer. In other words, out of every 100 women with the faulty BRCA1 gene, between 60 and 90 will develop breast cancer in their lifetime and between 40 and 60 will develop ovarian cancer.
The faulty BRCA genes affect around 1 in every 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).
For more information, The Royal Marsden NHS Foundation Trust has produced a beginner's guide to BRCA1 and BRCA2 (PDF, 867kb).
Page last reviewed: 26/04/2018
Next review due: 26/04/2021