The Oncologist's Guide to Direct-to-Consumer Genetic Testing


Ellen T. Matloff, a certified genetic counselor and the president and CEO of, gives advice to oncologists on navigating direct-to-consumer genetic testing.

Ellen T. Matloff

Ellen T. Matloff

The Issue

It’s another busy clinic day and you are swamped. You walk into what should be a fairly routine consult, and that patient pulls out his iPad and shows you the result of his direct-to-consumer (DTC) genetic test results from 23andMe. He announces that he carries a mutation inMUTYH. He also downloaded his raw data, ran it through a third-party interpretation service, and has 3 single nucleotide polymorphisms that he would like to discuss with you. What do you do?

First, take a deep breath. Many have experienced this phenomenon, and soon we all will. Five years ago, you may have told this patient that DTC test results are not ‘real’ genetic test results, and that he should ignore them. But we now know that up to 60% of test results derived from raw data reads are accurate,1and that the accuracy is much higher for mutations that 23andMe has FDA clearance to return directly to consumers, which now includes the 3BRCA1/2variants common in those with Ashkenazi Jewish descent and the 2 common mutations inMUTYH. We, as health care providers, can no longer afford to ignore these test results, as they can yield meaningful results for the patient and his/her entire family.2

But it is difficult, if not impossible, for a busy oncologist to stay current on all of the DTC genetic testing offerings. Some DTC companies, like 23andMe, return a few health-related results that are likely to be correct, but must be repeated with a new DNA sample in a medical-grade laboratory before use in clinical care. And what test you choose to repeat can be complicated. For example, the NCCN recommendation for carriers of 1MUTYHmutation is to next sequence the entire gene,3in case the person has a second mutation, causingMUTYH-associated polyposis (MAP),a hereditary colorectal cancer syndrome.

Other companies, including 23andMe and, return raw data files at the consumer’s request that can be downloaded and interpreted by a third party like Promethease. These results definitely require verification with a new DNA sample in a medical-grade laboratory. A few DTC companies, like Color, are considered ‘medical grade,’ and those results likely do not require confirmation. However, the panels used by some of these companies do not include all of the genes that may be indicated, based on the patient’s personal or family history. Each of these result types has its own limitations and nuances, and requires different counseling. So how should an oncologist handle this ever-changing landscape of DTC genetic information?

First and foremost, do not ignore the result. You could be ignoring a test result that has true clinical meaning for your patient and his/her family.

Management Plan

  1. Acknowledge that you understand the desire to know more about one’s genetics in order to make more informed healthcare choices and that getting genetic test results back can be confusing, and sometimes frightening.
  2. Underscore that most DTC genetic testing is not as thorough, complete, or accurate as medical-grade testing, and that there are both false-negatives and false-positives because of these limitations. No conclusions should be drawn based on DTC genetic testing alone.
  3. Suggest that the patient speak to a certified genetic counselor who can review both the DTC test resultsandthe personal and family history in detail, to determine what confirmatory testing, or broader testing, is needed. If you do not have a genetic counselor on-site or nearby, or if the wait time is longer than desired, there are also multiple phone genetic counseling services that can speak to your patients.You can choose genetic counselors who specialized in DTC counseling.A few specialists include:
  4. Consider offering the patient an online resource,, where they can purchase a low-cost report that will help him/her better understand these results.
  5. Follow-up with the patient 3 months out to see if genetic counseling and confirmatory testing was completed. If not, encourage the patient to pursue this channel.
  6. Once the patient has been seen by a genetics professional, help them implement the suggested medical management plan.


More than 15 million consumers have now had DTC genetic testing and it is estimated that 100 million will have such testing by 2021.4Between DTC genetic testing, large population studies, and employer-initiated testing programs, the majority of our patients will come in to appointments with test results in hand within the next decade. Some of these test results will be inaccurate, and others will provide accurate insights into hereditary cancer risk, pharmacogenetics, and other information that will be critical in your management of the patient and the entire family. Oncologists will be critical in helping patients make sense of their genetic test results.

Ellen T. Matloff is a certified genetic counselor and the president and CEO of, a company that provides digital genetic counseling and updates for consumers and health care providers.


  1. Tandy-Connor S, Guiltinan J, Krempely K, et al. False-positive results released by direct-to-consumer genetic tests highlight the importance of clinical confirmation testing for appropriate patient care.Genet Med. 2018;20(12):1515-1521. doi: 10.1038/gim.2018.38.
  2. Matloff E. Healthcare providers can’t afford to ignore direct-to-consumer genetic testing. Forbes website. Published April 25, 2018. Accessed February 5, 2019.
  3. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Genetic/Familial High-Risk Assessment: Colorectal. National Comprehensive Cancer Network website. Version 1.2018. Published July 12, 2018. Accessed February 5, 2019. 
  4. Khan R, Mittelman D. Consumer genomics will change your life, whether you get tested or not.Genome Biol.2018;19(1):120. doi: 10.1186/s13059-018-1506-1.
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