Hereditary Breast Cancer: What You Can – and Can't – Learn from Genetic Testing

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Post-Mastectomy Breast Reconstruction Specialist Dr. Constance M Chen Answers Questions and Offers Tips.

Dr. Constance M Chen

It's important to understand what we can and cannot determine from genetic testing, which women should have the test, and what can be done to reduce the risk for those who have inherited a mutated gene.

The most significant risk factors for breast cancer are being a woman and growing older. Among women in the general population, about one in eight (12%) will develop breast cancer over the course of her lifetime. However, among women who inherit a specific mutation in the BRCA1 or BRCA2 gene, the risk is significantly higher. “Genetic testing can identify women who carry the harmful mutations,” says plastic surgeon and breast reconstruction specialist Dr. Constance M. Chen, “but these mutations are relatively rare in the general population and not every woman needs testing. It's important to understand what we can and cannot determine from genetic testing, which women should have the test, and what can be done to reduce the risk for those who have inherited a mutated gene.”

What are BRCA genes? How do they affect breast cancer risk?
The BRCA1 and BRCA2 genes produce proteins that help suppress tumors. These proteins play a role in repairing damaged DNA and maintaining the genetic stability of cells. When the genes mutate or are altered so they fail to produce the proteins or don't function properly, damaged DNA may not be repaired and cells are more likely to undergo further changes that can cause cancer. Specific inherited mutations in the BRCA1 and BRCA2 genes are associated with increased risk of breast and ovarian cancer and play a role in other cancers as well, such as pancreatic cancer, prostate cancer, and melanoma. The child of a parent whose mother or father carries the mutated gene has a one in two chance of inheriting it. Estimates are that 72% of women who inherit the BRCA1 mutation and 69% of those who inherit the BRCA2 mutation will develop breast cancer by the age of 80. In some cases, the risk for developing breast cancer can be over 86%.(1)

Who should be tested for BRCA mutations?
“Compared to 12% of women overall who will have breast cancer, the increased risk associated with BRCA mutations is very substantial,” says Dr. Chen. “Given the risk, it's natural to ask if all women should be tested. However, only about 1 in 400 people in the United States carry a BRCA1 or BRCA2 mutation.(2) Thus, only people whose personal or family history is associated with greater likelihood of carrying the mutation are typically tested.” Indicators of a possible genetic mutation include a family history of breast or ovarian cancer, breast cancer diagnosed before age 50, male breast cancer, and cancer in both breasts. An additional risk factor is ethnicity; the BRCA mutation has a higher prevalence in women of Ashkenazi Jewish, Norwegian, Dutch, and Icelandic descent.

If I've already had breast cancer, is there any reason for me to be tested?
Yes. If your personal or family history or ethnicity point to the likelihood of high risk of hereditary breast cancer, the results of genetic testing can help you be aware of your risk for other cancers, like ovarian cancer, and are important in helping other members of your family assess their risk.

If I test negative for harmful BRCA mutations, am I home free? Can I stop worrying about breast cancer?
“If only it were so,” says Dr. Chen. “About 90% of women who have breast cancer have no family history of the disease and no known genetic mutation to account for it. In the vast majority of cases, cancer is caused by spontaneous mutation, the aging process, or environmental factors, so a negative test for BRCA mutation is no guarantee that you will not develop breast cancer. All women should continue to have regular breast exams and mammograms.”

If I test positive for a harmful BRCA mutation, does that mean I will get cancer? What should I do?
A positive result significantly increases the risk of developing breast cancer. Many women in this position explore options for reducing their risk, the most effective of which is bilateral prophylactic mastectomy – the preventive removal of both breasts. According to the National Cancer Institute, women with harmful BRCA mutations who undergo prophylactic mastectomy can reduce their risk of developing breast cancer by 95%.“The risk reduction statistics are compelling,” says Dr. Chen, “but the decision to undergo prophylactic mastectomy is a difficult one. Those who are faced with this decision must weigh various medical and personal factors, including the breast reconstruction options that are available to them.”

Are there any other gene mutations that I should be aware of?
There are other genetic mutations like CHEK2, Lynch syndrome, PALB2, ATM, BRIP1, and others, which can also increase the risk of breast cancer. Talk with your doctor or genetic counselor about your individual circumstance.

“Testing for BRCA and other genetic mutations has come a long way in the twenty or so years that it has been available,” Dr. Chen concludes. “In combination with genetic counseling, it provides valuable information that can guide key decisions for women and their families. However, the test can only help assess risk. Neither positive nor negative results provide definitive answers about who will or will not get cancer. Women and their doctors must consider test results along with other personal and medical factors to determine their best course of action.”

(1) Kuchenbaecker KB, Hopper JL, Barnes DR, et al. Risks of breast, ovarian, and contralateral breast cancer for BRCA1 and BRCA2 mutation carriers. JAMA 2017; 317(23):2402-2416.

(2) National Cancer Institute. Genetics of breast and gynecologic cancers (PDQ®) - health professional version., 2018.

Constance M. Chen, MD, is a board-certified plastic surgeon with special expertise in the use of innovative natural techniques to optimize medical and cosmetic outcomes for women undergoing breast reconstruction. She is Clinical Assistant Professor of Surgery (Plastic Surgery) at Weill Cornell Medical College and Clinical Assistant Professor of Surgery (Plastic Surgery) at Tulane University School of Medicine.

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