November 13, 2017
By Bridget Oppong, MD, FACS
In 2013, Time magazine featured Angelina Jolie and her decision to have genetic testing and then double mastectomy. This prompted many women to question whether they too should get testing.
Cancer Genetics in General
In order to make an informed decision about whether or not to have genetic testing done, it is important to understand some basic information about how your genes are involved in the development of breast cancer. Each of your genes is comprised of a piece of DNA, which is composed of 2 strands twisted around each other to form a double helix. Each strand of DNA is constructed from millions of chemical building blocks called bases. These bases may be arranged in many sequences, and each sequence gives instructions to specific cells in your body, telling them how to function.
Genetic Mutations that Can Cause Breast Cancer
Cancers are the result of genetic mutations, or changes to cells in the body, that may be caused by any number of factors. Some mutations are inherited and some acquired from repeated exposure to certain types of radiation or harmful chemicals. The two most common genetic mutations associated with breast cancer are known as BRCA1 and BRCA2. They are linked to the largest increase in lifetime risk for breast cancer. According to the National Cancer Institute, “Specific inherited mutations in BRCA1 and BRCA2 increase the risk of female breast up to 80% and ovarian cancers, and they have been associated with increased risks of several additional types of cancer. Together, BRCA1 and BRCA2 mutations account for about 20 to 25 percent of hereditary breast cancers and about 5 to 10 percent of all breast cancers. In addition, mutations in BRCA1 and BRCA2 account for around 15 percent of ovarian cancers overall.”
Women with the BRCA1 or BRCA2 gene are at a higher risk for:
- Breast cancer at an earlier age
- Breast cancer in both breasts
- Ovarian cancer
There are a number of other genetic mutations that are associated with breast cancer, but BRCA genes are by far the most common cause of family-related breast cancer.
Source: National Breast Cancer Foundation, Inc.®
Are Genetic Mutations for Breast Cancer More Common Among Some People?
The short answer is yes. For example, people of Ashkenazi Jewish descent have a higher prevalence of harmful BRCA1 and BRCA2 mutations than people in the general U.S. population. Other populations with a higher frequency of mutations in these genes include those of Norwegian, Dutch, and Icelandic descent.
Who Should Get Genetic Testing and How is it Performed?
To help determine who should be screened, doctors use the following guidelines to assess family history and other factors associated with an increased likelihood of having a harmful mutation in breast genes:
- Breast cancer diagnosed before age 50 years.
- Cancer in both breasts in the same woman.
- Both breast and ovarian cancers in either the same woman or the same family.
- Multiple breast cancers.
- Two or more primary types of BRCA1- or BRCA2-related cancers in a single family member.
- Cases of male breast cancer.
- Ashkenazi Jewish ethnicity.
Typically, a blood or saliva sample is needed to perform the test and results can take about a month.
Prior to testing, it is generally advised that patients considering genetic testing for mutations in the BRCA1 or BRCA2 genes talk to a genetic counselor before any testing is done. A genetic counselor will:
- Perform a hereditary cancer risk assessment based on an individual’s personal and family medical history.
- The appropriateness of genetic testing.
- The medical implications of a positive or a negative test result.
- The possibility that a test result might not be informative.
- The psychological risks and benefits of genetic test results.
- The risk of passing a mutation to children.
- Explain the specific test(s) that might be used and the technical accuracy of the test(s).
What Do Results of Genetic Testing for Breast Cancer Reveal?
Results of gene mutation testing for BRCA1 and BRCA2 will either show a positive result, a negative result, or may be uncertain:
- Positive Result—reveals that a person has inherited a known mutation to breast genes that increases their likelihood of developing breast cancer. A positive result does not mean that an individual will absolutely get breast cancer; in fact, many will never develop cancer. It simply means that their chances of getting it are heightened.
People with a positive result for harmful mutations to the BRCA1 or BRC2 genes may not develop cancer themselves, but their children each have a 50% chance of inheriting the mutation. It also reveals that that person’s siblings have a 50% chance of having inherited the same mutation.
- Negative Result—can be a bit more confusing to understand. If the person receiving the negative result has a close blood relative who is known to carry the gene mutation for breast cancer, then the person being tested did not carry the mutation and cannot pass it on to their children. They are considered to have the same risk as the general population.
A negative result may be less clear if the person tested does not know if they have a close family member with a gene mutation or if they have a mutation that is unable to be detected by current testing. For this reason, people may wish to consult with a genetic counselor to prepare themselves for results that are not completely certain.
- Uncertain or Ambiguous Results—a result may find a mutation in the BRCA1 or BRCA2 genes that has not been associated with breast cancer in the past, but is not yet known whether it carries additional risk of developing the disease. Approximately 10% of women who underwent mutation testing had this kind of result.
A strong family history of breast or ovarian cancer may suggest a genetic mutation (especially BRCA 1 or 2) causing cancer. Talking with your doctor can help you determine whether or not genetic testing is the right decision for you and your family.
National Breast Cancer Foundation, Inc.®: www.nationalbreastcancer.org
National Cancer Institute: www.cancer.gov