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. 

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.