About 5% to 10% of breast cancers are thought to be hereditary, caused by abnormal 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.
We’ve known for many years that mutations in the BRCA1 and/or BRCA2 genes are linked to a higher risk of breast cancer. 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. Now, we also know that other gene mutations are linked to breast cancer, including mutations in the PALB2, TP53, PTEN, and the BRIP1 genes.
More than 500 researchers from around the world collaborated on two studies that discovered 72 genetic variants that are associated with a higher risk of breast cancer:
- 65 of the variants are associated with a higher risk of breast cancer in general
- 7 of the variants are associated specifically with a higher risk of hormone-receptor-negative breast cancer
One study was published online on Oct. 23, 2017 by the journal Nature; the other also was published online on Oct. 23, 2017 by the journal Nature Genetics. Read the abstract of:
- “Association analysis identifies 65 new breast cancer risk loci”
- “Identification of ten variants associated with risk of estrogen-receptor-negative breast cancer”
In these studies, the researchers used the term “genetic variant” instead of “genetic mutation.”
The large team of researchers that did the studies is known as the OncoArray Consortium. To do the study, they analyzed genetic information from 275,000 women; 146,000 of the women had been diagnosed with breast cancer. The researchers looked at DNA at more than 10 million sites across the women’s genome, asking whether the DNA sequence in women diagnosed with breast cancer was different than in women who weren’t diagnosed with breast cancer.
A genome is an organism’s complete set of DNA, including all of its genes.
Individually, each of the newly identified genetic variants increases the risk of breast cancer only slightly -- by about 5% to 10%. Still, because the genetic variants are common and their effects on risk are multiplied when a woman has more than one of the variants, the combined effect may be dramatic. The effects of the variants also can be increased by other lifestyle factors that increase breast cancer risk, such as being overweight and smoking cigarettes.
"Taken together, these risk variants may identify a small proportion of women who are at three-times increased risk of breast cancer," said Peter Kraft, of the Harvard T.H. Chan School of Public Health and one of the study’s authors, in an interview.
Women who are found to have a number of these newly identified genetic variants would likely benefit from starting screening earlier than age 50.
"Using data from genomic studies, combined with information on other known risk factors, will allow better breast cancer risk assessment, therefore helping to identify a small but meaningful proportion of women at high risk of breast cancer," said Jacques Simard, of Université Laval in Canada and another study author. "These women may benefit from more intensive screening, starting at a younger age, or using more sensitive screening techniques, allowing early detection and prevention of the disease. At the same time, this personalized information will also be useful to adapt screening modalities for women at substantially lower risk."
If you have a strong family history of breast cancer, yet you and/or your family members had genetic testing years ago and tested negative for a BRCA1 or BRCA2 mutation, you may want to talk to your doctor about the two studies reviewed here and ask if having a newer multigene panel test makes sense for you.
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.