Most inherited cases of breast cancer are associated with two abnormal genes: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two). It’s been estimated that women with an abnormal (also called mutated) BRCA1 or BRCA2 gene have up to an 85% risk of developing breast cancer by age 70. These women’s risk of ovarian cancer also is higher than average.
A large study suggests that a woman’s risk of breast and ovarian cancer may vary depending on the type of mutation a woman has and where the mutation is located on the BRCA1 or BRCA2 gene.
The study was published in the April 7, 2015 issue of The Journal of the American Medical Association. Read the abstract of “Association of Type and Location of BRCA1 and BRCA2 Mutations With Risk of Breast and Ovarian Cancer.”
"We've made a lot of progress toward understanding how to reduce the cancer risks associated with inherited mutations in BRCA1 or BRCA2 mutations, but until now, little has been known about how cancer risks differ by the specific mutation a woman has inherited," said Timothy R. Rebbeck, Ph.D., professor of epidemiology and associate director for population science at the Perelman School of Medicine's Abramson Cancer Center at the University of Pennsylvania. Dr. Rebbeck was the lead author of the study. "The results of this study are a first step in understanding how to personalize risk assessment around a woman's specific mutation, which can help guide carriers and providers in the cancer prevention decision making process."
Genes are particles in cells, contained in chromosomes, and made of DNA (deoxyribonucleic acid). DNA contains the instructions for building proteins. And proteins control the structure and function of all the cells that make up your body.
Think of your genes as an instruction manual for cell growth and function. Abnormalities in the DNA are like typographical errors. They may provide the wrong set of instructions, leading to faulty cell growth or function. In any one person, if there is an error in the gene, that same mistake will appear in all the cells that contain the same gene. This is like having an instruction manual in which all the copies have the same typographical error.
In this study, the researchers looked at the records of more than 31,000 women known to have an abnormal BRCA gene:
- 19,581 women had a BRCA1 mutation
- 11,900 women had a BRCA2 mutation
They analyzed whether the type of mutation or the location of the mutation was linked to breast cancer risk, ovarian cancer risk, or both.
Among women with an abnormal BRCA1 gene:
- 46% (9,052 women) were diagnosed with breast cancer
- 12% (2,317 women) were diagnosed with ovarian cancer
- 5% (1,041 women) were diagnosed with both breast and ovarian cancer
- 37% (7,171 women) had never been diagnosed with cancer
Among women with an abnormal BRCA2 gene:
- 52% (6,180 women) were diagnosed with breast cancer
- 6% (682 women) were diagnosed with ovarian cancer
- 2% (272 women) were diagnosed with both breast and ovarian cancer
- 40% (4,766 women) had never been diagnosed with cancer
In the BRCA1 gene, the researchers found three locations where mutations were linked to breast cancer and one location where mutations were linked to ovarian cancer.
In the BRCA2 gene, the researchers found a number of locations where mutations were linked to breast cancer and three locations where mutations were linked to ovarian cancer.
The researchers explained that the results of this study suggest that women who have a specific type and location of BRCA mutations that are common in women of Ashkenazi Jewish descent have a higher risk of breast cancer (69%) and a lower risk of ovarian cancer (26%) than has been previously thought.
The results of this study are very interesting and could some day help women with an abnormal BRCA1 or BRCA2 gene make decisions about risk reduction steps, including taking hormonal therapy medicines or preventive surgery. Still, more research is needed before doctors understand the risk associated with different mutations and how the differences might affect women’s risk reduction choices as well as standards of care.
If you know you have an abnormal breast cancer gene, you may be considering taking steps to keep your risks of breast and ovarian cancer as low as they can be. There are many lifestyle choices you can make, including:
- maintaining a healthy weight
- exercising regularly
- limiting or avoiding alcohol
- eating nutritious food
- never smoking
There are also more aggressive steps you can take, including:
- a more aggressive screening plan, starting at an earlier age
- hormonal therapy to block the effect of estrogen on breast tissue or reduce the amount of estrogen in the body
- removing the healthy breasts and/or ovaries (prophylactic mastectomy and/or prophylactic oophorectomy)
For more information on BRCA1 and BRCA2 genes, as well as all the risk-lowering steps you can take if you have an abnormal version of one or both of these genes, visit the Breast Cancer Risk Factors: Genetics page in the Breastcancer.org Lower Your Risk section.
Editor’s Note: This article was updated on Jan. 24, 2019, with updated information on cancer risk associated with BRCA mutations.