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Breast cancer genes

It is possible to be born with a gene fault (mutation) that increases the risk of breast cancer. If you have a gene fault it doesn't mean you will necessarily get cancer. But it means that you are more likely to develop breast cancer than the average person.

How much breast cancer genes increase your risk

The first breast cancer gene faults to be found were BRCA1 and BRCA2. Between 45 and 90 out of every 100 women carrying BRCA genes will get breast cancer at some point in their lives (between 45% and 90% lifetime risk of breast cancer). Genetic tests are available to women with a high risk of having changes in BRCA1, BRCA2, or two other genes called TP53 and PTEN.

Genetic testing

You can have a genetic test if you have a strong family history of breast cancer. Ask your GP for a referral to a specialist breast clinic. If they think that your risk is high, they will refer you to a specialist genetics service. 

To be tested, you usually need to have a living relative with breast cancer, and they need to be tested first. Some labs can do a test without having blood from a relative but this is less likely to find the fault. It is important to understand that no test is 100% accurate and genetic tests can sometimes miss the fault.

 

CR PDF Icon You can view and print the quick guides for all the pages in the About breast cancer section.

 

 

Why faulty genes increase risk

A cell needs to have a number of mistakes in its genetic code before it becomes cancerous. Doctors call these mistakes faults or mutations. Most of these gene mutations develop during our lifetime. They can occur due to substances we come into contact with that cause cancer. Or they can happen because of mistakes that cells make when copying their genetic code before dividing into two new cells. 

Most of these abnormal cells die or are killed off by your immune system. It usually takes many years to gather enough genetic mistakes, so this is one of the reasons that cancer is generally more common as we get older.

But it is possible to be born with an inherited gene fault that may increase the risk of cancer. Having an inherited faulty gene doesn't mean that you will definitely get cancer. But it means that you are more likely to develop cancer than the average person.

 

Types of faulty genes

The first breast cancer gene faults to be found were BRCA1 and BRCA2. Between 45 and 90 out of every 100 women carrying BRCA genes will get breast cancer at some point in their lives. This means that they have between 45% and 90% lifetime risk of cancer. These genes also increase breast cancer risk in men. 

We know of other genes that significantly increase a woman's risk of breast cancer. They are called TP53 and PTEN. Genetic tests are available to women with a high risk of having changes in these genes

  • BRCA1
  • BRCA2
  • TP53
  • PTEN genes

Researchers have found other common genes that can slightly increase a woman's risk of developing breast cancer. No tests are available for these genes yet but they include

  • CASP8
  • FGFR2
  • TNRCP
  • MAP3K1
  • rs4973768
  • LSP1

Rare genes that can also increase breast cancer risk slightly include

  • CHEK2
  • ATM (ataxia telangiectasia mutated)
  • BRIP1
  • PALB2

No individual tests are available for these genes yet. But if you are having a test for the BRCA genes they may find changes in one of these genes. 

 

What lifetime risk means

Lifetime risk can be quite difficult to understand. 1 in 8 women in the UK will develop breast cancer during their lifetime. But the risk is small in younger women and increases as they get older. Women with a faulty gene have a higher risk of developing breast cancer than people of the same age. But if you are 30, your risk of breast cancer is going to be much lower than if you are 80, whether or not you have a faulty gene.

There is detailed information about definite risk factors for breast cancer in this section, including what is meant by having a family history.

 

How genetic tests work

It is only possible to have a test for BRCA1, BRCA2, TP53 or PTEN if you have a strong family history of breast cancer. Most people also need to have a living relative with breast cancer. This is because looking for a gene fault is a bit like looking for a single spelling mistake in a very long book. Your relative needs to be tested first to try to find out which fault on the breast cancer genes might run in your family. This is called the mutation search and can take a few weeks or months. If a faulty gene is found the researchers can then look for that same gene fault in you. This is called predictive testing.

Some labs can test the genes without having blood from a living relative, but this is less likely to find the fault. It is important to remember that no test is 100% accurate and any gene test can miss the fault. So, if your test is negative, this means that the tests didn’t find a gene mutation. It doesn't necessarily mean that there isn’t one there. 

With particular groups of women, there are very common specific gene faults. Ashkenazi Jewish women tend to have one of 3 very particular gene mutations. Specialists in breast cancer gene testing know where these mutations are in the gene. So it is much easier to check to see if you carry one of them. If you are Ashkenazi Jewish, you can have tests for these mutations.

 

Who should have tests

In the UK, guidelines published by the National Institute for Health and Care Excellence (NICE) say that women should only be referred to a specialist genetics services for gene testing if they are likely to have a high risk of developing breast cancer. 

NICE defines a high risk as having a 1 in 3 chance of getting breast cancer at some point in your life. Or a greater than 1 in 12 chance of getting breast cancer before the age of 50. The guidelines outline the different family situations that could mean you are at high risk. Generally, they look at

  • The age your relatives were diagnosed with breast cancer (the younger they are, the more likely there is to be a faulty gene in the family)
  • Whether anyone had cancer in both breasts
  • If there are men in your family who have had breast cancer
  • If there is also ovarian cancer in the family

The affected family members must be close, blood relatives of yours and must all be from the same side of the family (so either your mother's relatives OR your father's). You can read the public information on familial breast cancer on the NICE website.

 

Getting a test

To get a genetic test, you need to ask your GP for a referral to a specialist breast clinic. If they think you probably do have a high risk of breast cancer, they will refer you to a specialist genetics service. There, the staff will talk to you about your risk and discuss the test with you. The test result takes a few weeks, sometimes longer, to come back.

Before you decide whether or not to go ahead with the test, the staff in the clinic will make sure that you have good information to take away, read, and think about. Having a test can have a big impact on you and other members of your family. The clinic staff will try to answer all the questions you have about the test. There’s no rush and you can take as long as you need to make up your mind whether to go ahead or not.

Even if you know it is possible, finding out that you have a high risk of breast cancer is still likely to come as a shock. You need to be sure that you want to know the test result before you go ahead. And you also need to be sure that you will be able to decide what you will do if you have a faulty gene. Everyone is different and there is no right or wrong way to feel about this. 

The important thing is that you feel you have been given enough information to make the right choice about whether to have the test. Talk it over with a good friend or relative. Or if you feel you need to talk with your genetics specialist again, you can get back in touch with them.

 

Having a test

You have to give a blood sample. You can find information about NHS gene testing labs on the UK genetic testing network website. You can look on their database to see which services are offered by labs close to you.

You can have gene testing privately. It is still best to have a living relative with breast cancer so that they can be checked for all the most common gene faults first. You can have a test without having a living relative with breast cancer tested, but the result won't be as reliable. If it comes back negative, you still don't know for sure whether there is a gene mutation in your family or not.

It is important to be careful and make sure that you use a reputable company when finding private medical services on the web. Even if you are sure that you have found a reliable company, you really need to talk this over with a breast specialist or genetics specialist before going ahead.

 

The result

The most accurate way to find a faulty gene is to have a test after a faulty gene has already been found in one of your relatives who has breast cancer. The genetics lab will then look for this specific fault in your genes and can say definitely whether it is there or not.

A positive result means that you carry a known breast cancer gene. As we have seen, this means that you have an increased risk of breast cancer. 

A negative result means that you do not carry the same gene fault that was found in your relative. So you have the same risk of cancer as other people in the population. A very rare possibility is that you could have a different breast cancer gene mutation, but this is unlikely.

 

If you have a positive test result

There are options if the test shows that you have a known faulty breast cancer gene. You can

Have regular breast cancer screening

Screening increases the chance of a breast cancer being picked up early enough to cure it. Depending on your age, you may be offered regular mammograms, breast ultrasound or breast MRI scans.

Having surgery to remove your breasts (and possibly ovaries)

Having surgery is an option. Some women choose to have both breasts removed and immediate surgery to create new breasts (breast reconstruction). This greatly reduces the chance of breast cancer but does not completely reduce the risk. This type of surgery is called prophylactic mastectomy or preventive mastectomy.

Your medical team may also advise you to have your ovaries removed. Some breast cancer gene faults increase the risk of ovarian cancer too. As many as 2 out of 3 women who carry the BRCA1 or 2 genes will get ovarian cancer by the age of 75. A 2009 overview looked at all the studies that have been done into removing the ovaries and fallopian tubes to reduce breast cancer risk in women who have BRCA gene changes. The overview showed that this surgery reduced the risk of breast cancer in these women by 50%. This operation is called prophylactic oophorectomy.

Take medicines to lower your risk

Another option is taking a drug to lower your risk of developing breast cancer. Tamoxifen is a drug that has been used to treat breast cancer for more than 35 years. It works by stopping oestrogen from triggering hormone receptors in breast cancer cells. Raloxifene is a drug used to treat osteoporosis. Research has found that these drugs can also help to prevent breast cancer in women at high risk. 

The National Institute for Health and Care Excellence (NICE) has approved tamoxifen and raloxifene for women at high or moderate risk of developing breast cancer. NICE says that women with an increased risk should talk to their doctor about taking either tamoxifen or raloxifene for 5 years as a possible way of lowering their risk. Both of these drugs have side effects including increasing the risk of developing blood clots and strokes. So, NICE do not recommend them if you have had a blood clot or are at risk of developing one. Tamoxifen also slightly increases the risk of womb cancer. 

The IBIS 2 trial reported in 2013 that taking anastrozole (Arimidex) for 5 years can reduce the risk of developing breast cancer by 50% in women at high risk.  

There is information about research looking into drugs which may prevent breast cancer on the page about research into preventing and diagnosing breast cancer. Making a decision about what to do is not easy. It can help to find out as much information as possible about your risk and the different options as well as the pros and cons of each.

 

More information about breast cancer genes

There is more information about faulty breast cancer genes on the page about research into finding and preventing breast cancer. You can also go to the Cancer Research UK welcome page and search for 'breast cancer genes' to find further information on our website.

If you would like to check your own breast or ovarian cancer risk you can use the OPERA online interactive tool.

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Updated: 25 July 2014