1. Breast cancer in families
2. How does breast cancer start?
3. What causes breast cancer?
4. Inherited altered genes (including BRCA1 and BRCA2)

1. Breast cancer in families

If you or one of your close relatives has been diagnosed with breast cancer, you may have concerns about whether breast cancer runs in the family (sometimes called hereditary breast cancer). 

A small number of people have an increased risk of breast cancer because of their family history. However, most breast cancers are not inherited and do not increase the lifetime risk for other family members.

Breast cancer is the most common cancer in the UK, so even if you have a relative with breast cancer, it doesn’t necessarily mean you’re more likely to develop it yourself.

Back to top

2. How does breast cancer start?

Breast cancer starts when cells in the breast begin to divide and grow in an abnormal way.

All cells contain genes that tell them how to grow and function. Sometimes a change can occur in a gene that means the cells begin to function in an abnormal way. This is known as an altered gene (you might also hear this called a gene change, fault or mutation).

Altered genes can be either inherited or acquired.

  • Inherited altered genes are passed down from one of our parents.
  • Acquired altered genes develop due to a combination of things such as getting older and environmental and lifestyle factors.

Although breast cancer is very common, only a small percentage of cases are due to inheriting an altered gene.

For more information on genes and cancer see the Cancer Research UK website. 

Back to top


3. What causes breast cancer?

Most breast cancers are caused by a combination of many different things

While the exact causes are still unknown, research has shown that some things can increase or decrease the likelihood of getting breast cancer. These are called 'risk factors'. Being a woman and getting older are the biggest risk factors for developing breast cancer.

A small number of people have an increased risk of developing breast cancer because they have a significant family history. This may be because an altered gene that increases the risk of breast cancer runs in the family.

If you are worried about your family history you may be able to have a family history risk assessment.

Back to top

4. Inherited altered genes (including BRCA1 and BRCA2)

People who have inherited an altered gene (usually known as gene carriers) will be at a high risk of developing breast cancer and possibly other cancers. Around 5% of women with breast cancer have inherited an altered gene.

The most common inherited altered genes that increase the risk of breast cancer developing are called BRCA1 (BReast CAncer1) and BRCA2 (BReast CAncer2). Inheriting an alteration in a gene called TP53 (tumour protein p53) also increases the risk, although this is much rarer.

Some genetic conditions that are caused by other rare inherited altered genes also increase the risk of breast cancer, although not by as much as the BRCA1/2 or TP53 altered genes, these are:

  • Peutz-Jegher syndrome (STK11 altered gene)
  • Cowden’s syndrome (PTEN altered gene)
  • hereditary diffuse gastric (stomach) cancer (E-cadherin (CDH1) altered gene).

If one of these conditions runs in your family, you will also be managed as being at high risk for developing breast cancer.

Having an inherited altered gene will increase your risk of developing breast cancer significantly, but it doesn’t necessarily mean you’ll get breast cancer. Other things such as age, lifestyle and environmental factors also contribute to the likelihood of a cancer developing. Find out more about breast cancer risk factors.

There are a number of other genes that have been shown to increase the risk of developing breast cancer, but more research is needed to know how much the risk is increased and how to manage this risk.

Find out about genetic testing and cancer risks for gene carriers

Back to top

Last reviewed: March 2017
Next planned review begins underway

Your feedback