BRCA, the breast cancer gene

In May 2013, the breast cancer gene (BRCA) entered public discourse when Angelina Jolie told the world that she had undergone a preventative double mastectomy with reconstruction.

BRCA1 and BRCA2 (BReast CAncer) have become the best-known genes linked to breast cancer risk.

Each of us have two copies of BRCA1 and BRCA2 genes, which are involved with “cell growth, cell division, and the repair of damage to DNA.” Should a gene mutate, “cells are more likely to develop additional genetic alterations that can lead to cancer.”

Only about one in 400 (0.25%) of the population has mutated BRCA1 or BRCA2 genes.

BRCA genes and cancer

About 7 out of 100 women in the general U.S. population will develop breast cancer by the time they turn 70. Only about 1% of women in the US will develop ovarian cancer by age 70.

According to the Stanford Medicine Cancer Institute, women who inherit a mutation in the BRCA1 gene have a 47-85% probability of developing breast cancer by age 70. These women have a 39-46% probability of developing ovarian cancer.

Women who inherit a mutation in the BRCA2 gene have a 40-85% probability of developing breast cancer by age 70. These women have an 11-27% probability of developing ovarian cancer.

Stanford has developed a BRCA Decision Tool for patients and health care providers to use to guide risk management.

This snapshot illustrates the difference in risk for women age 40-44 who have the mutated BRCA1 gene versus women who don’t:

BCRA decision tool
For women aged 40-44, who do not have the mutated BRCA gene and no screening, the risks at age 70.
BRCA decision tool
For women aged 40-44, who have the mutated BRCA1 gene and no screening, the risks at age 70.

 

The National Cancer Institute makes it clear, however, that “other characteristics of a particular woman can make her cancer risk higher or lower than the average risks.”

Although BRCA gene mutations raise individual risk, they are  linked to a minority of breast cancers (~5-10%) and ovarian cancers (~15%).

Who is at risk of carrying the gene?

Although harmful BRCA1 and BRCA2 gene mutations are relatively rare in the general population, some populations are at higher risk of carrying the mutation:

  • People of Ashkenazi Jewish descent, which includes most Jews living in the United States
  • Dutch, Icelandic and Norwegian peoples
brca mutations by ethnic groups
From A Guide to Women’s Health, 2nd Edition; Tolu Oyelowo and Judith Johnson; May 2017; page 50

About 1-in-4 Jewish women who developed breast cancer by age 41 have one of these BRCA mutations.

In December 2013, the U.S. Preventive Services Task Force recommended that women who have family members with cancer of the breast, ovarian, fallopian tube, or peritoneal be evaluated to determine if they have a harmful mutation in one of these genes.

Other risk factors include:

  • A male relative with breast cancer
  • A family member who has both breast and ovarian cancers
  • A family member with bilateral breast cancer
  • A relative with ovarian cancer
  • A relative with a known BRCA1 or BRCA2 mutation

The Affordable Care Act considers genetic counseling and BRCA1 and BRCA2 mutation testing for individuals at high risk as a covered preventive service.

Two important things to consider about genetic testing:

Both men and women who inherit a harmful BRCA1 or BRCA2 mutation, whether or not they develop cancer themselves, may pass the mutation on to their sons and daughters. Each child has a 50 percent chance of inheriting a parent’s mutation.

If a person learns that he or she has inherited a harmful BRCA1 or BRCA2 mutation, this will mean that each of his or her full siblings has a 50 percent chance of having inherited the mutation as well.

However, only about 10% of women diagnosed with breast cancer have a family history of the disease.

 

Learn more at KnowBRCA.

 

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