Can at-home DNA tests predict cancer?

A genetic counselor discusses the limitations of at-home genetic tests.

By: Larissa Risty .

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Over the past few years, people have had access to at-home tests that can tell them about their DNA and ancestry. Lately, some of these tests have begun to also provide results on genetic risks for certain diseases or cancers.

One that has been in the news recently is 23andMe, which the FDA cleared to market its detection of specific breast cancer mutations.

That may sound like an appealing option for women who may be concerned about getting breast cancer. But it’s important to understand exactly what the test does — and does not — really indicate.


Will an at-home DNA test be able to tell me if I’m going to get breast cancer?

Not definitively. At a basic level, the 23andMe genetic test looks for three mutations of the BRCA1 and BRCA2 genes. Mutations in BRCA1 and BRCA2 can put you at an increased risk of Hereditary Breast and Ovarian Cancer Syndrome.

There are thousands of mutations that can cause HBOC Syndrome — the 23andMe test can identify three of them.

These three specific mutations are more common in people of Ashkenazi Jewish descent. About 2 percent of the Ashkenazi Jewish population carry one of these mutations, but they aren’t the most common BRCA1 and BRCA2 mutations in other populations.

So the vast majority of the general population aren’t carriers of the three mutations the test looks for.


Does a negative result on a genetic test mean I’m not going to get breast cancer?

No. Tests that have a very limited genetic scope can falsely make you think you’re in the clear — or the opposite. It’s not looking at the whole picture, or giving you the context of what tests in clinical settings could do.

In a clinical setting, a genetic test that looks all the way through the BRCA1 and BRCA2 genes could pick up thousands of different mutations that might cause Hereditary Breast and Ovarian Cancer Syndrome.

Of all the diagnosed cases of breast cancer, only 5 to 10 percent of them are caused by an identifiable hereditary trait. In 90 to 95 percent of breast cancer cases, genetic testing for the known hereditary cancer genes does not provide an answer.

A negative genetic test doesn’t mean you’re never going to get cancer. You’ll still want to talk with a professional to assess your risk, and to understand what the best screening approach would be.


What should I do if I’m concerned about getting breast cancer?

If you’re worried about your health — whether it’s cancer or cognitive diseases or other conditions that may run in your family — a clinical setting will be the most reliable place to assess your risk.

Before you get a genetic test, meeting with a genetic counselor first can answer your questions, or go over any test results you may have already received.

When I meet with patients, I also always ask about their personal health history, and about their family. Questions like who in your family has had this type of cancer or disorder, what age were they diagnosed, were there any environmental exposures that may have exacerbated their risk — these can give clues about a family’s health across multiple generations. From that, a pattern may emerge about your risk of getting cancer.

There are many risk factors for cancer that can potentially layer on one another, making it difficult to find a definitive cause.

A thorough family history can help pinpoint the most appropriate genetic test for you.

Sometimes there isn’t a genetic test that would give concrete answers, but your family has a strong history of cancer.

So we may instead recommended a change in screening frequency or timing, which your primary care doctor can incorporate into your regular visits. Or we may refer you to a specialist to discuss procedures, medications or other options to help reduce your risk.


Is an at-home DNA test worth doing?

It’s great that this type of testing is becoming widely available to people. With these direct-to-consumer tests, they’re affordable, easy and on-demand.

Especially with the ancestry side of the tests, it’s really interesting. You get to see what genetics you have from different parts of the world to understand more about who you are and give you more information on that DNA background. It can be fun, and pretty fascinating.

On the genetic risk side, the results you get may be difficult to interpret, or lack that medical perspective that would help you understand what it means for you.

If you’re trying to diagnose a disease or pinpoint a genetic risk factor, going down a clinical path for that genetic analysis will make sure your full personal and family history is included, and it can help in interpreting the results and understanding what you should do next. That thoroughness and follow-up really make a difference.



Posted In Cancer, Genetics, Health