Genetic tests done at home may be more convenient and less expensive than tests done through doctors’ offices or genetic counselors, but a study suggests that these tests are giving many people false-negative results for genetic mutations linked to breast, ovarian, and colorectal cancer. For some ethnic minorities, the risk of missing a cancer-linked mutation could be as high as 100%.
A false-negative result means that the genetic test says a person has no mutation linked to cancer, when in reality the person does have a cancer-linked mutation.
The research was presented on Oct. 17, 2019, at the American Society of Human Genetics Annual Meeting. Read the abstract of “Limitations of direct-to-consumer genetic screening for hereditary breast, ovarian, and colorectal cancer risk.”
Gene mutations linked to breast cancer
Two of the most well-known genes that can mutate and raise the risk of breast and/or ovarian cancer are BRCA1 and BRCA2. Women who inherit a mutation in either 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 also have an increased risk of breast cancer, especially if the BRCA2 gene is affected, and possibly of prostate cancer.
About 5% to 10% of breast cancers are thought to be hereditary, meaning the cancer is linked to mutations in genes passed from parent to child.
You are substantially more likely to have a genetic mutation linked to breast cancer if:
- You have blood relatives (grandmothers, mother, sisters, aunts) on either your mother's or father's side of the family who had breast cancer diagnosed before age 50.
- There is both breast and ovarian cancer on the same side of the family or in a single individual.
- You have a relative(s) with triple-negative breast cancer.
- There are other cancers in your family in addition to breast, such as prostate, melanoma, pancreatic, stomach, uterine, thyroid, colon, and/or sarcoma.
- Women in your family have had cancer in both breasts.
- You are of Ashkenazi Jewish (Eastern European) heritage.
- You are Black and have been diagnosed with breast cancer at age 35 or younger.
- A man in your family has had breast cancer.
- There is a known breast cancer gene mutation in your family.
About at-home genetic tests
Over the past decade or so, at-home genetic testing or “DNA testing” has become available, including kits for at-home testing of BRCA1, BRCA2, and other inherited genetic mutations that increase lifetime risk of breast cancer (and possibly other cancers). These at-home tests are also called direct-to-consumer genetic tests.
In some cases, the test companies require you to provide the name and contact information of your doctor, who must approve your eligibility for the test. If you don’t have a doctor, the companies can provide one who will review your case and order the test. Some of the companies can connect you with a genetic counselor if you don’t have one.
The company 23andMe offers the Personal Genome Service Genetic Health Risk Report for BRCA1/BRCA2 (Selected Variants). This test does not require a doctor to order it — you can purchase it directly from the company. The test only detects three out of more than 1,000 known BRCA mutations, and genetic counseling is not offered with the test.
The main advantages of at-home genetic testing are convenience and cost, as these tests tend to be less expensive than hospital-ordered tests. The at-home tests cost about $200–300. Still, there can be some major disadvantages to these at-home tests:
- Some of these tests may only look for mutations in the BRCA1 and BRCA2 genes. We know there are many more genetic mutations linked to breast and ovarian cancer, including PALB2, CHEK2, and PTEN.
- Some insurance plans may only cover genetic testing once in your lifetime. So if you use insurance coverage for a test that only looks for BRCA1 and BRCA2 mutations, your insurance may not cover additional tests to look at a broader range of genes in the future.
- There usually is no genetic counseling up front. A genetic counselor or your doctor can help you decide which genetic test is right for you and offer ongoing, in-depth information.
About this study
Because the number of people using at-home genetic tests has increased dramatically in the past few years, researchers wanted to know if the test results were accurately identifying people with mutations.
The study was done by Invitae, a California-based genetic testing company.
The researchers looked at two groups, or cohorts, of people who were referred to Invitae by their doctors for comprehensive genetic testing for mutations linked to cancer:
- Cohort 1 included 270,806 people with a personal or family history of any cancer who were screened for mutations in the MUTYH gene. The MUTYH gene makes an enzyme involved in DNA repair. Mutations in the MUTYH gene are linked to cancers of the colon and rectum.
- Cohort 2 included 119,328 people with a personal or family history of breast or ovarian cancer who were screened for mutations in the BRCA1 and BRCA2 genes.
After all the people in each cohort had genetic testing through Invitae, the researchers looked to see how many people had the particular mutations that would be found by common at-home genetic tests.
Of the 5,929 people in cohort 1 who had a MUTYH mutation linked to cancer based on Invitae genetic test results, only 4,552 people had one of the two specific mutations that would be found by at-home tests.
The researchers calculated that if people had received only at-home genetic testing, 40% of people who had mutations in both copies of the MUTYH gene would have been missed. So some people who had two mutations linked to cancer in the MUTYH genes, which gives a nearly 100% lifetime risk of developing colon cancer, would have received false-negative results if they had only at-home genetic testing.
In cohort 2, 4,733 people were found to have a BRCA1 or BRCA2 mutation linked to cancer by the Invitae test. Of these people, only 12% had one of three mutations that would be found by at-home genetic tests. Overall, mutations in 19% of Ashkenazi Jewish people and 94% of non-Ashkenazi Jewish people would not have been found if the people had only at-home genetic testing.
When the researchers looked at at-home genetic testing by ethnicity, they said the outcomes concerned them.
Mutations in BRCA1 and BRCA2 genes would have been missed in:
- 98% of Asians
- 99% of Blacks
- 94% of Hispanics
- 94% of Caucasians
Mutations in the MUTYH gene would have been missed in:
- 100% of Asians
- 75% of Blacks
- 46% of Hispanics
- 33% of Caucasians
“We did expect there to be … some clinical false-negative rate, [but] I was honestly surprised that it was as high as it was,” said Edward Esplin, M.D., clinical geneticist at Invitae who presented the research, in an interview. He was concerned that people may not understand exactly what at-home genetic tests test for and could be interpreting the results to mean they don’t have any mutations linked to cancer when they actually do.
What this means for you
If your personal or family history of cancer or your ethnicity suggests that you are likely to have a genetic mutation linked to breast cancer, it makes sense to talk to your doctor or a licensed certified genetic counselor about your history and ask if having genetic testing makes sense for you and your unique situation.
If you decide to use an at-home genetic test, it’s important to understand which mutations are included in the test and what the results might mean.
“The main caution is to be aware of what you’re being tested for ahead of time,” said Cristina Nixon, a licensed certified genetic counselor with Main Line Health and member of the Breastcancer.org Professional Advisory Board. “Don’t just do the test, but actually talk to somebody about what this test has included and what the results might mean. You need to be aware of what the implications are should one of the genes come back positive [for a mutation].”
For more information on testing for genetic mutations linked to breast cancer, types of genetic tests, and how results are reported, visit the Breastcancer.org Genetic Testing pages.
Want expert insights? Hear Cristina Nixon explain the benefits and drawbacks of at-home genetic tests in a Breastcancer.org podcast.
Written by: Jamie DePolo, senior editor
Reviewed by: Brian Wojciechowski, M.D., medical adviser
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