Genetic testing is used to identify particular mutations that someone may be born with that may increase their risk of developing certain diseases, like breast cancer. Some people may choose to have genetic testing to understand their risk of developing breast cancer, such as those with a family history of the disease. Other people who already have breast cancer may choose to get genetic testing to understand their risk for developing other cancers, including additional breast cancers or ovarian cancer.
Genetic mutations common in breast cancer
Approximately 5% to 10% of all breast cancers are caused by inherited genetic mutations. Two of these genetic mutations – BRCA1 and BRCA2 – are tumor suppressor gene mutations. Tumor suppressor genes normally manage cell growth and death and help prevent the development of cancer. However, if tumor suppressor genes are mutated, cancer cells can multiply out of control. The BRCA1 and BRCA2 mutations confer an increased risk of breast cancer in women and men, as well as an increased risk of ovarian cancer in women. These genetic mutations are considered “high penetrance,” because they frequently lead to the development of cancer.1,2
Other genetic mutations that are less common but may also slightly increase a person’s risk of breast cancer include PALB2, TP53, PTEN, CDH1, and STK11.3
Who should consider genetic testing?
Understanding the genetic mutations which may or may not be present can provide powerful information to help a person take steps to reduce their risk of developing cancer. People may consider genetic testing to help assess breast cancer risk, especially those who4:
Have a family member with a known BRCA1 or BRCA2 mutation
Have previously developed breast cancer prior to age 50
Are of Ashkenazi Jewish ancestry
In addition, the National Comprehensive Cancer Network recommends for women who have developed breast cancer at a young age (age 50 or less) to have genetic testing.5 This is because patients with BRCA1 and/or BRCA2 genetic mutations have an increased risk of being diagnosed with breast cancer at a young age.
Options to reduce risk
For people who discover that they do have a BRCA1 or BRCA2 mutation that puts them at higher risk for developing breast cancer, they may choose to take medication or have surgery to reduce their risk. The use of medications to prevent breast cancer is called chemoprevention. Currently, the U.S. Food and Drug Administration (FDA) has approved two selective estrogen receptor modulators (SERMs) to lower breast cancer risk: tamoxifen (brand names: Nolvadex® and Soltamox™) and raloxifene (brand name: Evista®). SERMs block the action of estrogen in some tissues, such as breast tissue. Tamoxifen can be used by women who are premenopausal or postmenopausal, and raloxifene is approved only for use in women who are postmenopausal.6,7
Surgeries to reduce the risk of cancer include prophylactic mastectomy, in which both breasts are surgically removed, or prophylactic oophorectomy, in which the ovaries are surgically removed. Prophylactic mastectomy can reduce the risk of developing breast cancer by approximately 95%. However, it is not a guarantee. In a mastectomy, it is impossible to remove all breast cells, and the small amount of breast tissue that is left could still develop into breast cancer. Removal of the ovaries can help reduce the risk of ovarian cancer and can also help reduce the risk of breast cancer, as it greatly reduces the amount of estrogen in the body.6,8
Genetic testing is a personal decision and must be considered thoughtfully. Genetic counselors are trained professionals who can help guide and support those who are considering or choose to get genetic testing. Genetic counselors can help patients make informed decisions about what next steps to take.9
How does breast cancer start? American Cancer Society. Available at https://www.cancer.org/cancer/breast-cancer/about/how-does-breast-cancer-form.html. Accessed 8/31/18.
Breast cancer treatment (PDQ) – patient version. National Cancer Institute. Available at https://www.cancer.gov/types/breast/patient/breast-treatment-pdq. Accessed 8/31/18.
Genetics of breast and gynecological cancers (PDQ) – health professional version. National Cancer Institute. Available at https://www.cancer.gov/types/breast/hp/breast-ovarian-genetics-pdq. Accessed 8/31/18.
Do you need genetic testing for breast cancer? MD Anderson Cancer Center. Available at https://www.mdanderson.org/publications/focused-on-health/october-2014/genetic-testing-for-breast-cancer.html. Accessed 8/31/18.
Rosenberg SM, Ruddy KJ, Tamimi RM, et al. BRCA1 and BRCA2 mutation testing in young women with breast cancer. JAMA Oncol. 2016;2:730-736.
Breast cancer: risk factors and prevention. Cancer.net from ASCO. Available at https://www.cancer.net/cancer-types/breast-cancer/risk-factors-and-prevention. Accessed 8/31/18.
Deciding whether to use medicine to reduce breast cancer risk. American Cancer Society. Available at https://www.cancer.org/cancer/breast-cancer/risk-and-prevention/deciding-whether-to-use-medicine-to-reduce-breast-cancer-risk.html. Accessed 8/31/18.
Preventive surgery to reduce breast cancer. American Cancer Society. Available at https://www.cancer.org/cancer/breast-cancer/risk-and-prevention/preventive-surgery-to-reduce-breast-cancer-risk.html/. Accessed 8/31/18.
Who are genetic counselors? National Society of Genetic Counselors. Available at https://www.nsgc.org/page/whoaregcs. Accessed 8/31/18.