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BRCA gene mutations

Most breast and ovarian cancers are not hereditary. Some women have a family history of breast cancer, but only a small number of these are due to an inherited gene that increases their risk of cancer.

  • There may be a genetic link to breast or ovarian cancer if there is a higher incidence in women who have a family history (especially in first-degree relatives) of these cancers.
  • Mutations in the genes BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2) increase a woman’s risk of developing breast or ovarian cancer.
  • BRCA mutations account for about 5% of all breast cancers and 4%–11% of all ovarian cancers.
  • Genes are not the only factor that affects cancer risk, so not every woman who inherits a BRCA gene mutation will develop breast or ovarian cancer.

The most common form of hereditary breast and ovarian cancers (HBOC) are due to mutations in the BRCA genes. BRCA1 and BRCA2 are tumour suppressor genes, which are genes that normally prevent cancer from developing. Researchers have identified hundreds of mutations in the BRCA genes. Many of these are linked to an increased chance of developing breast and ovarian cancer. Other, rarer hereditary gene mutations are also associated with an increased risk of breast and ovarian cancer, but these are not discussed here.

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Chances of inheriting a BRCA mutation

Both men and women can inherit a mutated BRCA gene from either their mother or father. People who have the gene mutation can also pass it on to their children. If one parent has the mutation in 1 of the 2 copies of the BRCA gene, a child has a 50% chance of inheriting the gene mutation. This also means there is a 50% chance that a child will not inherit the gene mutation.

The likelihood that breast or ovarian cancer is associated with an inherited BRCA1 or BRCA2 mutation is highest in families that have:

  • a history of family members with breast or ovarian cancer
  • early onset breast cancer in 1 or more female relatives (before age 50)
  • both breast and ovarian cancer in a single relative
  • family members who develop cancer in both breasts (bilateral breast cancer)
  • a male relative with breast cancer
  • Ashkenazi (Eastern European) Jewish ancestry

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BRCA mutations in certain populations

Researchers have identified specific gene mutations in certain ethnic groups. People of Ashkenazi (Eastern European) Jewish ancestry have about a 2.5% (or about 1 in 40) chance of having a mutated BRCA gene. This is considerably higher than in the general population.

Other ethnic and geographic populations also have a somewhat higher rate of BRCA gene mutations, including people of Norwegian, Dutch and Icelandic ancestry.

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Risk of cancer

Breast cancer in women with a BRCA mutation is more likely to occur at a younger age (usually before menopause) compared to sporadicsporadic1. Occurring at random or by chance. 2. Occurring at scattered, intermittent or random intervals. breast cancer. Women with BRCA mutations often develop breast or ovarian cancer before age 50.

A woman’s lifetime risklifetime riskThe chance or probability that a person will develop a particular disease over his or her entire life. of developing breast or ovarian cancer is greatly increased if she has a BRCA mutation, compared to women who don’t have a BRCA mutation.

  • Women with a mutated BRCA1 or BRCA2 gene have a 40%–85% chance of developing breast cancer in their lifetime.
  • Women with a mutated BRCA1 gene have a 25%–65% chance of developing ovarian cancer in their lifetime.
  • Women with a mutated BRCA2 gene have a 15%–20% chance of developing ovarian cancer.

BRCA gene mutations can also increase the risk of developing some other cancers, but these are much less common than breast or ovarian cancer.

  • Mutations in the BRCA1 and BRCA2 genes have been associated with an increased risk of Fallopian tube and primary peritoneal carcinoma in women. These mutations are also associated with a higher risk of pancreatic cancer in both sexes.
  • Men with a mutated BRCA gene have an increased risk of male breast cancer. This risk is most strongly associated with a mutation in the BRCA2 gene. A man with a BRCA2 gene mutation has a 5%–10% chance of developing breast cancer in his lifetime. Men with a BRCA gene mutation also have an increased risk of developing prostate cancer.

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Genetic testing

Women with breast or ovarian cancer, as well as a significant family history of breast or ovarian cancer, may be the first in a family to be tested to see if they have a gene mutation. A healthcare professional will determine if women are eligible for genetic screening. If they qualify for testing, they will likely be referred to a genetic program where geneticists or genetic counsellors do more detailed assessments. In Canada, genetic testing to see if a person carries a BRCA gene mutation is done through hereditary (familial) cancer programs. A woman has to meet certain criteria before she has genetic testing for hereditary breast and ovarian cancer.

Genetic counselling is recommended before and after testing. A blood sample is required for genetic testing. Other family members may then wish to have genetic counselling and genetic testing to see if they also carry the mutation, if one is identified.

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Reducing your risk and early detection

Women who know that they have a BRCA gene mutation (they tested positive for a BRCA1 or BRCA2 mutation) should talk to their doctor about taking steps to help reduce their risk of cancer and to find it early.

  • For women with a BRCA mutation, breast cancer prevention strategies may include prophylactic surgeries (such as mastectomy and oophorectomy) and chemoprevention drugs.
  • Ovarian cancer prevention strategies for women with a BRCA mutation may include prophylactic salpingo-oophorectomy and chemoprevention drugs.
  • Women with a BRCA gene mutation may need to be screened or tested at an earlier age and more often than women with average risk for breast and ovarian cancer. For more information, go to screening for breast cancer and early detection of ovarian cancer.

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Photo of John Dick Dr Dick identified a gene mutation that could be the trigger for leukemia.

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