If you have been diagnosed with breast cancer and have a family history of the disease or other factors that put you at high risk of having a genetic mutation, you may be interested in genetic testing.
About 5% to 10% of breast cancers are thought to be hereditary, caused by genetic mutations passed from parent to child. Three of the most well-known genes that can mutate and raise the risk of breast and/or ovarian cancer are BRCA1, BRCA2, and PALB2. Women who inherit a mutation, or abnormal change, in any of these genes — from their mothers or their fathers — have a much higher-than-average risk of developing breast cancer and/or ovarian cancer. Men with these mutations have an increased risk of breast cancer, especially if the BRCA2 gene is affected, and possibly of prostate cancer. Many inherited cases of breast cancer have been associated with mutations in these three genes.
In the past, genetic tests used technology called genotyping, which looked for the most common mutations in only the BRCA1 and BRCA2 genes. As technology has advanced, next generation sequencing now makes it possible for genetic tests to look for many different mutations in a number of genes. Some labs can look for mutations in up to 80 genes.
A study has found that most women now have multigene testing after a breast cancer diagnosis, but this genetic testing is happening later in the treatment plan than testing for only BRCA1 or BRCA2 mutations. Genetic testing later in the care process means the results aren’t being used to help make surgery decisions.
The research was published online on May 10, 2018 by JAMA Oncology. Read the abstract of “Uptake, Results, and Outcomes of Germline Multiple-Gene Sequencing After Diagnosis of Breast Cancer.”
Using information from the SEER databases, the researchers identified 1,316 women who lived in Los Angeles and Georgia who were diagnosed with early-stage breast cancer from 2013 to 2015 and had also had genetic testing.
The SEER databases are large registries of cancer cases from sources throughout the United States maintained by the National Institutes of Health.
The researchers looked to see which type of genetic testing the women had:
- In 2013, the rate of BRCA-only testing was 74.4% and the rate of multigene testing was 25.6%.
- In 2015, the rate of BRCA-only testing was 33.5% and the rate of multigene testing was 66.5%.
"We found that over a 2-year period there was a remarkably rapid replacement of the older two-gene BRCA1/2-only test with broader multiple-gene panel tests," said Allison Kurian, M.D., of the Stanford University School of Medicine and lead author of the study. "It's become more common after 2013 thanks to advances in technology and, actually, changes in patent law."
In 2013, the U.S. Supreme Court ruled that human genes couldn’t be patented. Until that ruling, Myriad Genetics held patents on the BRCA1 and BRCA2 genes for more than a decade and made the only U.S. test for mutations in the two genes. After the ruling, many new genetic tests came on the market. It’s now much easier to test many genes for a lower cost than it used to be to test only the two BRCA genes.
The researchers were concerned because more women who had multigene testing had the testing after surgery, compared to women who had BRCA-only testing:
- 32.5% of the time, multigene testing happened after surgery
- 19.9% of the time, BRCA-only testing happened after surgery
"That needs to be addressed so we can get the results earlier to guide surgical decision-making," Dr. Kurian said.
Compared to BRCA-only testing, multigene testing was more likely to find any genetic mutations linked to cancer.
Rates of genetic mutations linked to cancer found by multigene testing in:
- high-risk women: 12%
- average-risk women: 4.2%
Rates of genetic mutations linked to cancer found by BRCA-only testing in:
- high-risk women 7.8%
- average-risk women: 2.2%
Women who had multigene testing were not more likely to have prophylactic mastectomy than women who had BRCA-only testing. The highest rate of prophylactic mastectomy was in women who tested positive for a BRCA1 or BRCA2 mutation.
"We did not see a strong signal that people who had the multiple-gene tests were much more likely to have an extensive surgery -- like a double mastectomy -- and I think that, in many ways, is reassuring," Dr. Kurian said.
"In general, multigene panel tests yield more clinically useful results and are rapidly becoming the norm," Dr. Kurian added. "Newly diagnosed women should ask their doctors whether they may be appropriate candidates for genetic testing."
If you’ve been diagnosed with breast cancer, you may want to talk to your doctor or a licensed certified genetic counselor about your diagnosis and your family history and ask if having a multigene panel test makes sense for you. No matter which genetic test you have, it is important to know exactly which genes and mutations the test is analyzing. A licensed certified genetic counselor or your doctor can help you understand the test and accurately interpret the results.
For more information on genetic testing, including types of genetic tests and how results are reported, visit the Breastcancer.org Genetic Testing pages.
For more information on genes and genetic mutations linked to breast cancer, as well as all the risk-lowering steps you can take if you have a genetic mutation, visit the Breast Cancer Risk Factors: Genetics page in the Breastcancer.org Lower Your Risk section.