Hereditary breast cancer

This information is about breast cancer that runs in a family. This is called hereditary breast cancer.

You may be interested in this information because you are concerned about your risk of breast cancer due to a family history or because you have had breast cancer in the past and also have a family history.

Even though this information is mainly aimed at women, it may also be relevant to men.

It is important to understand that most breast cancers are not hereditary. Breast cancer is more commonly linked to other risk factors. 

 General information on breast cancer and its risk factors can be found in our breast cancer information  pages.

What is hereditary breast cancer?

Hereditary breast cancer occurs when a faulty gene is passed on from either parent. This greatly increases the chance that cancer will develop, but people can carry such genes and not develop breast cancer. It is important to remember that hereditary breast cancer is rare. 

What does hereditary mean?

Hereditary means that a genetic condition can be carried by the genes that pass from parents to children.  

Experts believe that between 5–10% of breast cancer cases are caused by changes that have been passed on in certain genes. 

What are genes?

Genes are a special set of instructions inside the cells of our bodies that parents pass on to their children. Genes contain information, telling our bodies how to grow and work. Genes are also responsible for many things, like the colour of our eyes and the size of our feet.

How is breast cancer linked to genes?

Our bodies grow with a set of instructions from our genes. Sometimes a gene in a cell develops a fault. As a result that cell may grow abnormally and become cancerous. 
If you inherit a faulty gene at birth it means that cells throughout the body are much more likely to develop changes leading to cancer.
The instructions of each gene are like a code. Sometimes the code changes and is different to a normal gene. For example, imagine the code for a normal gene is: 1-2-3-4-5
A cancer gene passed down through a family may have a mistake, giving a slightly different code: 1-2-3-7-5
The mistake in the gene means it will give a different instruction to the cell it controls. As a result, it can make it grow in a different way. Only when a serious change occurs in the gene does a problem occur. 
There are a number of genes that can cause breast cancer when they contain such faults. The two most commonly tested for are called BRCA 1 and BRCA 2.

Faults in these genes are associated with high risks of developing breast or ovarian cancer.

BRCA 1 stands for breast cancer gene 1 and BRCA 2 stands for breast cancer gene 2. 

Who might be at risk of having hereditary breast cancer?

You may be at risk of hereditary breast cancer if members of your family have had breast cancer. The risk is higher if they are close relatives or if many family members have been affected.
Some of the risk factors for hereditary breast cancer are: 
1. If a breast cancer gene has been identified in a family (e.g BRCA1, BRCA2)
2. One 1st degree relative (a very close relative - mother, father, sister, brother, child) aged under 40 at diagnosis with breast cancer.
3. Two relatives affected by breast cancer on the same side of the family aged under 50, one a first degree relative.
4. Three 1st or 2nd degree relatives (close relatives, such as grandparents, uncles and aunts, nieces and nephews) on the same side of the family diagnosed before the age of 60.
5. One relative with breast cancer and one relative with ovarian cancer on the same side of the family.
6. A  1st or 2nd degree relative with bilateral breast cancer if the first cancer diagnosed before the age 50.
7. A male relative with breast cancer
If you have inherited a breast cancer gene you will not definitely develop cancer, but you have a higher risk of developing cancer compared to other people. 

What are 1st and 2nd degree relatives?

1st degree relative, 2nd degree relative and 3rd degree relative are terms used to describe how close to you a family member is. If you have relatives with a cancer diagnosis, the possible risk to you is greater, the closer they are related to you. A combination of close and more distant relatives may also pose a risk.
1st-degree relative
  • A first-degree relative can be your mother or father, sister/ brother or child. These are your closest relatives and you share 50 percent of your genes with them.
2nd-degree relative
  • A second-degree relative is defined as a blood relative, which includes your grandparents, grandchildren, aunts, uncles, nephews, nieces or half-siblings.
3rd-degree relative
  • A third-degree relative is defined as a blood relative, which includes your first-cousins, great-grandparents or great grandchildren.

What should I do if there is a history of breast cancer in my family? 

If you are concerned about having a family history of breast cancer, it is important to discuss these concerns with your GP. 
You will be asked to give more information on family members who have or have had breast, ovarian and other cancers. Details will be required regarding the age at which the family member first got cancer and the type of cancer. If the GP thinks you are at risk, he or she can refer you to the national centre for medical genetics clinic.
A genetic test can be done at the National Centre for Medical Genetics (NCMG) at Our Lady's Hospital for Sick Children at Crumlin, St. James Hospital Dublin and The Mater Hospital, Dublin.
NCMG outreach clinics are run at University College Hospital in Galway, Cork University Hospital in Cork and UHL Limerick at regular intervals throughout the year. 
There may be waiting lists for appointments.

What happens if I am referred to the National Centre for Medical Genetics

If you have been referred to the National Centre for Medical Genetics you will be sent a questionnaire asking for details of your family history of breast, ovarian and other cancers. This questionnaire is returned by post, and evaluated by the clinical team. If you are judged to be at low risk, you will be reassured by letter, and will only be seen if you are very concerned. 
Women judged to be at high risk will be invited to attend one of the breast cancer clinics for further investigation and possible predictive genetic testing.
Your personal risk of developing breast cancer will be defined, if possible, as low, medium or high risk.

What does my risk group (low / medium / high) mean?

Low risk: This means your breast cancer risk is about the same as the rest of the population. You should continue to be breast aware, and attend the National Breast Screening Programme when invited. If you are judged to be at low risk, you will be reassured by letter, and will only be seen if you are very concerned. 
Medium risk: This means you have a medium risk compared to the rest of the population. Depending on your age, you may be invited for a mammogram and offered screening at a younger age or more regularly. You will be given support and information that is relevant to your needs.
High risk: This means you have a high risk of developing breast cancer compared to the rest of the population. If you are at high risk you need expert advice on how to reduce your risk and what measures you need to consider in terms of screening, surgery, lifestyle and medication. Women judged to be at high risk will be invited to attend one of the breast cancer clinics for further investigation and possible predictive genetic testing.
If you inherit a known breast cancer gene, it does not mean you will definitely develop breast cancer. 
Whatever your risk group, it is important to continue being breast aware and to report any changes to your doctor.
It is also important to update your family history and to let your doctor know if any of your family develop breast, ovarian or other cancers.

What is genetic testing?

Genetic testing means your blood is tested to see if you have a faulty gene that may increase your risk of breast cancer or that may be the cause of a previous cancer diagnosis. The test involves taking a blood sample.
This sample is sent to a specialist laboratory to try and find the particular fault in the gene. Once you have given a sample of blood it can take many weeks to see whether or not you have a faulty gene.
The search for a fault is like looking for a single spelling mistake in a very large book.
If you do require genetic testing everything will be clearly explained to you.
You will also be given a chance to think about how you might feel if the test does show you are carrying a breast cancer gene. There will be support for you after you get the result too.
Genetic testing is currently only suitable for people with a high-risk family history or if there is a known genetic mutation in a family.
What kinds of genetic testing are possible?
You may have genetic testing for two reasons:
  1. Diagnostic testing
If you or a family member have or have had breast or ovarian cancer and a family history of one or both of these cancers a diagnostic genetic test may be done to see if there is a fault on the gene. A test can show whether mutations in the BRCA1 and BRCA2 are present. Finding such mutations means a higher risk of developing these cancers. Finding a mutation also makes it possible to offer tests to adult relatives to see if they are at risk of developing cancer (predictive genetic testing). 
            2.   Predictive genetic testing
If a BRCA1 or BRCA2 mutation has been found in your family, you may be offered predictive gene test. This testing of relatives unaffected by cancer is called predictive genetic testing.   It is an individual choice for each family member whether or not they wish to be tested.                       

Call our Cancer Nurseline

Freephone 1800 200 700 to talk to a specialist cancer nurse.
It's open Monday-Thursday from 9am to 6pm and Friday from 9am to 5pm.
Date Last Reviewed: 
Friday, July 17, 2015