The average woman (without an inherited breast cancer gene abnormality) in the United States has about a 12% risk of developing breast cancer over a 90-year life span.
In contrast, women who have an abnormal BRCA1 or BRCA2 gene have up to an 85% risk of developing breast cancer by age 70. BRCA1 and BRCA2 abnormalities are found in 5% to 10% of all breast cancer cases in the United States. Other abnormal genes also have been thought to increase breast cancer risk, but these genes are less common than BRCA1 and BRCA2 and their link to breast cancer is not as clear.
In one study, researchers looked at more than 20,000 women diagnosed with breast cancer and more than 20,000 women without breast cancer to see if there were any abnormal genes that were more common in women with breast cancer. This would mean that these abnormal genes might be associated with breast cancer. Because people have so many genes (about 23,000), it's a kind of like looking for a needle in a haystack.
So far, the researchers found women with breast cancer were more likely to have an abnormal version of gene FGFR2, compared to women without breast cancer. At least 60% of the women studied had at least one abnormality on the FGFR2 gene. Women with one abnormality on the FGFR2 gene were found to be 20% more likely to develop breast cancer, compared to women without an abnormality on that gene. Women with two abnormalities on the FGFR2 gene were 60% more likely to develop breast cancer.
Abnormalities on the FGFR2 gene affect a substance called tyrosine kinase that plays a role in the development and growth of several types of cancer. So the link between this gene and breast cancer makes sense.
In two other large studies in Great Britain and the Netherlands, researchers found that abnormalities in or near three other genes (TNRC9, MAP3K1 and LSP1) also were found to be associated with breast cancer.
The findings from these studies are important, but it's too early to recommend women be screened for these abnormal genes. We need a better understanding of these abnormal genes and their link to breast cancer. Still, these results increase what's known about genetic abnormalities associated with an increased risk of breast cancer. These findings also may lead to new ways to detect and treat breast cancer in the future.
For more information on genes and breast cancer risk, visit the Breast Cancer Risk Factors: Genetics page.