Genetic factors

Most women who get breast cancer don’t have a history of breast cancer in their families. However, there is sometimes an inherited gene linking cancers in the same family. The genes most often found in inherited breast cancer are BRCA1 and BRCA2. If a family has an altered BRCA1 or BRCA2 gene, several close relatives may be diagnosed with breast cancer or related cancers, such as ovarian cancer.

You may be at an increased risk of breast cancer due to your family history. For example you have a close relative who developed breast cancer under the age of 40, a close male relative with breast cancer, or breast and ovarian cancer on the same side of the family.

If you’re worried about developing breast cancer because of your family history, speak to your GP. They can talk to you about risk and refer you to a clinical genetics service if necessary.

How does family history affect breast cancer risk?

Most breast cancers are not hereditary (caused by inherited cancer genes) and most women who get breast cancer don't have a family history of it.

If you have one female relative who developed breast cancer over the age of 40, your risk is unlikely to be very different from other women your age. However, sometimes breast cancer can run in families. In general, a family link is more likely when more members of your family have been diagnosed with breast cancer (or related cancers such as ovarian cancer). It is also more likely the younger they were when diagnosed and the more closely related they are.

Only a very small proportion of breast cancers (5 – 10%) are thought to be caused by a change (alteration) in a gene running in the family. The two genes that are most often found to be altered in hereditary breast cancer are called BRCA1 and BRCA2.

If a family has an altered BRCA1 or BRCA2 gene, usually several relatives on the same side of the family are diagnosed with breast cancer or related cancers. People in the family may also be diagnosed with cancers at a particularly young age.

BRCA gene alterations are more common in certain populations. If you have Ashkenazi Jewish ancestry and have relatives who've been diagnosed with ovarian or breast cancer, you may want to discuss your risk with your GP.

If you're concerned about your risk of breast cancer, visit your GP. They can talk to you about your family history and your risk.


Assessing family history

A family history of cancer is usually based on your close relatives, which includes your first-degree relatives.

First degree relatives are your parents, brothers, sisters and children. Close relatives are your first-degree relatives and also your grandparents, grandchildren, aunts, uncles, nieces and nephews.

Examples of a family history that may mean you have an increased risk of developing breast cancer include having:

  • one first degree relative who developed breast cancer under the age of 40
  • one first degree male relative (father, brother or son) with breast cancer
  • one first degree relative with cancer in both breasts
  • two close relatives (one of whom is a first-degree relative) on the same side of your family who developed breast cancer under the age of 60
  • three close relatives on the same side of your family who developed breast cancer at any age
  • breast and ovarian cancer on the same side of the family.

If any of the above apply to your family, or you’re worried about your risk, talk to your GP. They may be able to reassure you or refer you to a clinical genetics service or family cancer clinic.

A woman’s risk of breast cancer, based on her family history, may be estimated as average, moderate or high.

Average risk (near population risk)

This is also sometimes called population risk. It means your risk is the same or very similar to the risk for women who don’t have a family history of breast cancer. You’re more likely not to get breast cancer than to get it.

Moderate risk (raised risk)

This means your risk is higher than average but it’s unlikely that there is a breast cancer gene in the family. You are still more likely not to get breast cancer than to get it.

High risk

This means you have a high risk of developing breast cancer in your lifetime. However, it doesn’t mean that you’ll definitely get breast cancer. There may be a hereditary breast cancer gene in your family.

Back to Potential causes of breast cancer

Age, lifestyle and risk

Your risk of developing breast cancer may increase with age, alcohol intake, being overweight and smoking.

Hormonal factors

Your exposure to the hormones oestrogen and progesterone can affect your risk of developing breast cancer.