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How do breast cancer genes work?

Main points

  • When working normally, BRCA genes protect us from breast and ovarian cancer (and prostate cancer in men). When they are altered, they increase our chances of getting cancer.
  • Altered BRCA genes are passed down from our parents.
  • If you have an altered BRCA gene, your close family (sons, daughters, brothers and sisters) have a 50% (1 in 2 chance) of having the altered gene.
What are breast cancer genes?
  • Everyone has BRCA1 and BRCA2 genes. When they are working normally, they help to protect us from cancer. They are called cancer protection genes. They protect us from cancer by helping to repair damage or destroying damaged cells in our body.
  • Genes are passed down from our parents.
  • If someone has an altered BRCA gene, they have a higher chance of getting cancer. This does not mean that they will definitely get cancer.
  • Even if you have a strong family history of breast cancer, this does not mean you will definitely have an altered BRCA gene.
  • When someone has a strong family history of breast cancer but an altered BRCA gene is not found, the cancers may still be linked to genetics. Experts think there are genes which are linked to families that have not yet been found. Genetic tests will not always give you a clear answer about what is causing the increased chances of breast cancer within your family.
How are altered BRCA genes passed down through families?
  • Altered BRCA genes can be passed down from your Mother or Father.
  • If a mother or father has an altered BRCA gene, any children (boys and girls) have a 50% (1 in 2) chance of having the altered gene.
  • The diagram below shows how altered BRCA genes are passed down in families. Click to enlarge

altered gene

  • If you have an altered BRCA gene, your sisters and brothers and children will also have a 50% (1 in 2) chance of having the gene. If you have two children, one or both or none of them may have the altered gene.
  • If an altered BRCA gene was passed down from your Mother, her brothers and sisters would have a 50% (1 in 2) chance of having the gene. If an altered BRCA gene was passed down from your Father, his brothers and sisters would have a 50% (1 in 2) chance of having the gene.
  • If you have an altered BRCA gene, where possible, your Mother and Father should have genetic testing to see which side of the family the altered gene was passed down from. This will help to find out the chance of cousins, aunts and uncles having the altered gene.
  • Altered BRCA genes do not skip generations but not all individuals who have altered BRCA genes develop cancer. For instance, men have a low risk of getting breast cancer. This is because they have small amounts of breast tissue and low levels of female sex hormones. This can make it look like the altered BRCA gene has skipped a generation.
  • It is possible that you could be the first person in your family to have the altered BRCA gene, but this is extremely rare.
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