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What are BRCA1 and BRCA2?

BRCA1 and BRCA2 are genes. They both make proteins that repair DNA and suppress the growth of cancer. A mutation in the BRCA1 or BRCA2 gene means DNA damage cannot be repaired as well which increases the risk for cancer. We all have BRCA1 and BRCA2 genes. Men or women born with a BRCA1 or BRCA2 gene mutation have Hereditary Breast and Ovarian Cancer (HBOC).

How common is Hereditary Breast and Ovarian Cancer (HBOC)?

In the general population around 1/600 (0.25% to 0.17%) people are born with a BRCA1 or BRCA2 gene mutation. In individuals of Ashkenazi Jewish background around 1/40 (2.5%) are born with a BRCA1 or BRCA2 gene mutation. BRCA gene mutations are passed on from either a person’s mother or father. A person with a BRCA gene mutation has a 50% chance of passing it on to their children.

What does a family with Hereditary Breast and Ovarian Cancer (HBOC) look like?

A family with HBOC may contain the following history of cancer:

  • Multiple relatives on the same side of the family with breast/ovarian cancer.
  • A family member diagnosed with breast cancer before age 40.
  • A family member diagnosed with ovarian cancer at any age.
  • A family member diagnosed with cancer in both breasts OR with breast and ovarian cancer.
  • Breast/ovarian cancer in someone of Ashkenazi Jewish ancestry.
  • A male diagnosed with breast cancer.
  • A relative with a known gene mutation in BRCA1 or BRCA2.

Get more information


  • What is HBOC?
  • What is a gene mutation?
  • What genes are linked to HBOC?
  • What is my risk of inheriting a BRCA1 or BRCA2 mutation?


  • What is cancer?
  • What is hereditary cancer?
  • Hereditary vs. sporadic cancer
  • Signs of hereditary breast and ovarian cancer (HBOC)
  • Other hereditary cancers

Canadian Cancer Society

  • Chances of inheriting a BRCA mutation
  • BRCA mutations in certain populations
  • Risk of cancer
  • Genetic testing
  • Reducing risk and early detection

Contact information

For any questions related to content on this page, or if you would like to see any additional topics discussed, please contact the Cancer Genetics and High Risk Department

Phone: 416-480-6835

Fax: 416-480-5859

Email: occ.genetics@