When you hear “breast cancer screening” you probably think “mammogram.” Mammograms have been around for decades and are an extremely important tool in the early detection of breast cancer.
This is different from prevention, where the goal is to prevent breast cancer from developing in the first place. New research that allows women to know their personal risk of breast cancer can potentially prevent breast cancer by counseling women at increased risk on what they can do to reduce that risk.
The personalized approach to identify who is at increased risk takes into account not only clinical factors and family history but also integrates genomic factors — known as single nucleotide polymorphisms (SNPs). The combination of all these factors is the polygenic risk score — and it’s an exciting development.
Screening and prevention
For most women today, screening for breast cancer begins at age 40 with the first mammogram followed by the same test every 1 to 2 years. A mammogram is an X-ray image of the breasts done by compressing the breast tissue between two firm plates. Mammograms are recommended for nearly all women, regardless of their personal or family history of breast cancer. Women with strong family histories of early breast cancer may benefit from screening mammograms starting before age 40.
Women deemed at higher risk of breast cancer might also be screened with magnetic resonance imaging (MRI). And women with strong family histories of breast cancer may have genetic counseling and testing. With MRI, multiple images of the breasts are captured and combined, using a computer, to create detailed pictures. MRI is used to screen women at high risk of breast cancer, including those with a calculated lifetime risk of 20% or greater, a known high-risk gene change (mutation), or a personal history of prior radiation therapy to the chest.
Another differentiator for risk of breast cancer is genetic testing. Traditional genetic testing to assess for the presence of altered genes, including for altered BRCA1 and BRCA2 genes, is done via a blood test. The BRCA gene test isn’t routinely performed but is offered to women deemed likely to have an inherited gene change based on personal or family history of breast cancer or pathology.
Those with a positive test result for BRCA1 or BRCA 2 have a much higher risk of developing breast cancer than those who don’t have the gene change. But only 5% to 10% of women have a hereditary gene change, such as a BRCA1 or BRCA 2 gene change. We know that many women who receive a diagnosis of breast cancer do not have an identifiable hereditary gene alteration.
An even more-personalized approach to risk assessment and prevention
A more-advanced and personalized approach to breast cancer risk assessment is probably on the horizon: the polygenic risk score (PRS). The PRS has the potential to tell each woman her individual risk of breast cancer. This is a step toward teasing out who may need high level screening — or maybe less frequent screening. PRS is not yet in use in clinical practice; but in the future, it could be incorporated into standard breast cancer risk assessment risk calculator tools.
PRS combines information on up to 200 single nucleotide polymorphisms (SNPs) into a single risk score. SNPs are, in essence, “spelling mistakes” in the DNA sequence that are inherited from parents. Each individual SNP, however, has a minimal impact on the risk of disease. Taken in combination, this probably tells a different story.
A blood test is used to assess the SNPs, and this information is then integrated with the standard risk calculators to provide an individual polygenic risk score for a period of five years and 10 years and a lifetime risk score. PRS has been investigated in a multicenter study led by researchers from Mayo Clinic and CancerCare Manitoba. They used PRS to assess individual breast cancer risk in women and found that PRS could place individuals into different categories. Women with an increased polygenic risk score were more likely to take an anti-estrogen medication to reduce their risk of breast cancer compared with women with a low polygenic risk score.
These results indicate that PRS could be as powerful as other known factors for predicting breast cancer risk. Because it’s individualized, PRS can help women make better-informed decisions. This information may encourage women to adjust their screening strategies, dietary approaches and interest in medications to reduce the risk of future breast cancer.
The overall goal of all types of breast cancer risk assessment — including personalized stratification with PRS — is to improve the ability to predict who is at increased risk of breast cancer and potentially allow for a future with individually modified strategies and recommendations.
