What genetic testing didn’t tell me about my cancer

Even as a doctor, I didn't grasp what my DNA test meant. How can we expect consumers to understand the caveats?

Published June 24, 2018 2:00PM (EDT)

 (Getty/Photo Montage by Salon)
(Getty/Photo Montage by Salon)

"What do you share with Dad? This Father’s Day, celebrate your DNA connection with Dad."

This was the tag line of personal genomics company 23andMe’s marketing campaign for Father's Day. Now, a week later, dads are sending away for their DNA results. What will their gift really reveal about the genetic traits they have passed on to their children? In my case, it is a gene that puts both me and my father at high risk for cancer.

The U.S. Food and Drug Administration (FDA) approved the first direct-to-consumer genetic health risk test last year. As a doctor I see that as a truly amazing scientific advancement. Yet of course there are caveats.

Anyone can order 23andMe — with less than $150 and a small tube of saliva, you can learn much about your ancestry, where your family came from, and whom you might be related to. Even more than learning about your ancestry, you may be interested in the medical implications of the results — for example how well your body can handle certain drugs, or caffeine. Or whether you are at risk for allergies, heart disease… or even cancer.

Knowing this information seems like nothing but a positive on the surface. If you knew early in life you were predisposed for heart disease, it might prevail upon you to exercise more often and limit excessive indulgence in high-fat foods. Optimistically, there could be great benefits to that knowledge.

However, are you really prepared to learn that your 5-year-old daughter carries the BRCA gene? The gene that may put her at a 70 percent chance to have breast cancer and other cancers such as ovarian and pancreatic cancer?

Given the enormity of what our genetic code entails, we may want to weigh the consequences of knowing more about our DNA. And whether as consumers we can really handle what we might learn of the possible fate of ourselves and our children. How do we console the anxieties of a devastated father who logs into the website for his results late at night and finds out that he passed on one of the most feared cancer genes to his children? That father could have been my father.

Without the support of a health care provider giving context and guidance, how much knowledge is too much? It’s important for consumers to be able to connect with a medical professional in order to really understand the data they’re receiving and its context.

The 23andMe test is not intentionally misleading. But on the other hand, it’s important to understand that knowledge itself also has limits. You’ll only find out BRCA gene risks if both of your parents are of Jewish ancestry. That explains why when I read my 23andMe results, there was nothing about BRCA —  my Swiss-French ancestry made it unlikely, as did the fact that I had no other high-risk factors. Still, I do have the BRCA mutation and did get breast cancer.

As a physician, I understand clearly the scope of the BRCA testing offered by this specific test. Reading all the disclaimers carefully, I would have known that with my ancestry, any BRCA mutation I could harbor would not have been tested for.

However, even as a doctor, I did not completely grasp that when my 23andMe test came back as only a slightly increased risk for breast cancer, this would have no real meaning for me.

So how can we expect the general consumer to fully understand this?

We live in an increasingly information- and data-driven environment, and have access to huge opportunities for early medical interventions. Knowledge is usually a very good, highly empowering, tool with appropriate medical context and support. But as consumers, when ordering a test that claims to tell you about your cancer risk, it’s important to fully understand the limits of the information you’re receiving.

The FDA’s approval of the 23andMe test is an important landmark. The test offers a fascinating and hopefully useful and enlightening glimpse into one’s ancestry. Harmful BRCA mutations are worth knowing about, not least because the mortality they may mediate can be significantly reduced by preventative measures. When dealing with direct-to-consumer tests that may help address and/or raise important health issues, we as consumers need to fully understand the fine print.

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Dr. Pamela Munster is a breast cancer specialist and a leading researcher on BRCA mutations. She is the author of the forthcoming book "Twisting Fate: My Journey with BRCA — From Breast Cancer Doctor to Patient, and Back" (September 2018).


By Pamela N. Munster

Pamela N. Munster, MD, is a professor of medicine at the University of California, San Francisco, where she is leader of the Developmental Therapeutics Program/Helen Diller Family Comprehensive Cancer Center, director of Early Phase Clinical Trials Unit, and coleader of the Center for BRCA Research. She is the author of the forthcoming book, "Twisting Fate: My Journey with BRCA—From Breast Cancer Doctor to Patient and Back," out September 2018. In addition to her laboratory research, Dr. Munster focuses on developing novel strategies to treat patients with incurable cancers as an oncologist. She serves on multiple local, national, and international committees focused on developing new treatments for cancer, has published over two hundred articles, authored textbooks, and is a frequent lecturer. A native of Switzerland, she leads breast awareness campaigns in the US, UAE, and India.

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23andme Brca Mutation Breast Cancer Dna Genetic Testing Genetic Data Personal Data