About 5% to 10% of breast cancers are thought to be hereditary, caused by mutated genes passed from parent to child.
Genes are short segments of DNA (deoxyribonucleic acid) found in chromosomes. 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 a 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. A genetic error that causes harm is called a mutation.
Many inherited cases of breast cancer are associated with two gene mutations: BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two).
The average woman in the United States has about a 1 in 8, or about 12%, risk of developing breast cancer in her lifetime. Women who have a BRCA1 or BRCA2 mutation (or both) can have up to an 80% risk of being diagnosed with breast cancer during their lifetimes. Breast cancers associated with an abnormal BRCA1 or BRCA2 gene tend to develop in younger women and occur more often in both breasts than cancers in women without these abnormal genes.
Women with an abnormal BRCA1 or BRCA2 gene also have an increased risk of developing ovarian, colon, and pancreatic cancers, as well as melanoma.
Men who have an abnormal BRCA2 gene have a higher risk of breast cancer than men who don't -- about 8% by the time they're 80 years old. This is about 80 times greater than average.
Men with an abnormal BRCA1 gene have a slightly higher risk of prostate cancer. Men with an abnormal BRCA2 gene are 7 times more likely than men without the abnormal gene to develop prostate cancer. Other cancer risks, such as cancer of the skin or digestive tract, also may be slightly higher in men with abnormal BRCA1 or BRCA2 genes.
Still, it hasn’t been clear how much family history of cancer and the specific location of the BRCA1 or BRCA2 mutation affected the increase in risk at specific ages. An accurate risk assessment allows people and their doctors to use the best strategies to manage that risk, including preventive medicines or surgery.
A study has estimated the risk of breast and ovarian cancer by age, taking into account family history and mutation location for women with a BRCA mutation.
The research was published in the June 20, 2017 issue of the journal JAMA. Read the abstract of "Risks of Breast, Ovarian, and Contralateral Breast Cancer for BRCA1 and BRCA2 Mutation Carriers."
To do the study, the researchers analyzed the records of nearly 10,000 women with a BRCA1 or BRCA2 mutation:
- 6,036 women had a BRCA1 mutation
- 3,820 women had a BRCA2 mutation
The women ranged in age from 30 to 47 years.
When the study started, 4,810 of the women had been diagnosed with breast cancer, ovarian cancer, or both.
Half the women were followed for more than 5 years and half were followed for a shorter time.
- 426 women were diagnosed with breast cancer
- 109 women were diagnosed with ovarian cancer
- 245 were diagnosed with breast cancer in the opposite breast (contralateral breast cancer)
Using statistical analysis, the researchers found:
- Up to age 80, breast cancer risk was 72% for women with a BRCA1 mutation and 69% for women with a BRCA2 mutation.
- Rates of breast cancer diagnoses increased rapidly in early adulthood until about age 30 to 40 for women with a BRCA1 mutation and until about age 40 to 50 for women with a BRCA2 mutation. After those ages, breast cancer rates stayed stable until about age 80 for both mutations.
- Up to age 80, ovarian cancer risk was 44% for women with a BRCA1 mutation and 17% for women with a BRCA2 mutation.
- The risk of developing breast cancer in the opposite breast 20 years after first being diagnosed with breast cancer was 40% for women with a BRCA1 mutation and 26% for women with a BRCA2 mutation.
- Breast cancer risk went up as increasing numbers of first- and second-degree relatives were diagnosed with breast cancer for both BRCA1 and BRCA2 carriers. Women who had two or more first- or second-degree relatives diagnosed with breast cancer had double the risk of the disease compared to women who had no family history of breast cancer.
- The specific location of the BRCA1 or BRCA2 mutation affected the amount of increase in risk.
"Women with BRCA1/BRCA2 mutations are recommended to have their ovaries and fallopian tubes removed prophylactically to prevent ovarian cancer, but if they are premenopausal when they have the surgery, they will experience sudden menopause and be subject to long-term cardiovascular and bone health risks," said Breastcancer.org Professional Advisory Board member Mary Daly, M.D., Ph.D., of Fox Chase Cancer Center, in a comment on the study.
"Likewise, BRCA1/BRCA2 carriers who have a diagnosis of breast cancer are faced with the choice of just treating the affected breast or having a double mastectomy to prevent a second breast cancer," she continued. "Having a clear idea of their age-specific risk for a second breast cancer may help them make that decision. This information is useful in the clinical setting when counseling women about the options and timing of prophylactic surgery options."
If you know you have a gene mutation linked to a higher risk of breast cancer, 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.