BRCA1 & BRCA2: The Breast Cancer Genes

BRCA1 and BRCA2 are the most common breast and ovarian cancer predisposition genes. If a woman has an altered (or "mutated") form of either of these genes, this greatly increases the lifetime risks of both breast and ovarian cancer. In the general population, the chance that someone carries a BRCA1 or BRCA2 alteration is about 1 in 800 (1/8 of 1%).

Among individuals of Ashkenazi Jewish ancestry, the number is higher with about 1 in 40 (2.5%) carrying 1 of 3 specific BRCA1 or BRCA2 alterations that predisposes to breast and ovarian cancer.

While BRCA1 and BRCA2 gene alterations account for a substantial proportion of hereditary breast and ovarian cancers, it is likely that other breast cancer genes will be discovered.

Alterations in BRCA1 and BRCA2 are passed on equally by fathers and mothers to sons and daughters. Because we all have two copies of each gene, an individual with an alteration in BRCA1 or BRCA2 has a 1 in 2 (50%) chance of passing on the altered gene to each of his or her children.

Some people who carry an alteration in BRCA1 or BRCA2 never develop cancer. However, for women, the risks of breast and ovarian cancer are higher than average. Women with a BRCA1 alteration have a 50% to 85% chance of developing breast cancer and a 20% to 40% chance of developing ovarian cancer over a lifetime. Women with a BRCA2 alteration face a similar lifetime chance of breast cancer and about a 10% to 20% lifetime chance of ovarian cancer. There also appears to be a slightly increased risk for other cancers, including breast cancer in men.

"Red Flags" for Hereditary Breast and Ovarian Cancer Syndrome include:

  • Breast cancer before age 50
  • Ovarian cancer at any age
  • Male breast cancer at any age
  • Multiple primary cancers
  • Eastern Ashkenazi Jewish ancestry
  • Relatives of BRCA mutation carrier