23andMe and CRC Risk


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Update: Many patients have found us because they're curious about using 23andMe to check for colon cancer and rectal cancer. We're happy to say 23andMe's new MUYTH report includes links to Fight CRC's genetics resources, such as the Mini Magazine, to support patients in learning about hereditary colorectal cancer. Read more about their report here.

It's a popular gift: ancestry tests. Many people have been gifted the 23andMe DNA test. You’ve heard of Ancestry.com. Same idea, but along with exploring your family ancestry, 23andMe also allows you to explore your health and genetics.

23andMe has announced a new addition to their test: an addition that can inform consumers if they are at a heightened risk of colon or rectal cancer.

About the tests

On January 22nd, 2019, 23andMe announced a new addition to their test. It can now identify whether or not you have a specific gene variant that may increase the risk of developing colorectal cancer (CRC).

The Food and Drug Administration (FDA) approved the use of this test, which will soon be available for consumers.

What genetic variants does 23andMe look for?

23andMe tests look for two specific genetic variants that are located in the MUTYH gene. These two MUTYH variants are present in about 1-2 percent of individuals of Western European descent.

Individuals who inherit two MUTYH variants (one from each parent) have a condition called MUTYH-associated polyposis (MAP), which causes an increased risk for colorectal polyps and colorectal cancer.

Polyps that develop with MAP are usually adenomas, but can also include hyperplasic and sessile serrated polyps, which can be harder to detect during screening. There may be dozens, hundreds or thousands of polyps, however, some individuals with MAP may develop CRC without a significant number of polyps.

Risks of using 23andMe for genetic testing

The genetic tests from 23andMe may give a person a false sense of their overall colorectal cancer risk, as it only is designed to detect two specific mutations in the MUTYH genes.

The test does not include the genes associated with Lynch syndrome, which is the most common type of hereditary colorectal cancer, or any other genetic syndrome that could increase CRC risk. Lynch syndrome is caused by mutations in mismatch repair genes, including MSH2, MSH6, MLH1, and PMS2.

Deletions at the end of the EPCAM gene can 'turn off' the MSH2 gene, and also cause Lynch syndrome.

Should I use the 23andMe test?

Before you run out and order your test, consider the perspective: Hereditary cases of colorectal cancer are only about 5-10% of cases.

According to Heather Hampel, GI cancer genetic counselor at The Ohio State University,

This test can be very misleading. MUTYH mutations are very common in the general population (1 in 50) and I am concerned that people who are found to have one MUTYH mutation might erroneously think that they have a significant risk for colorectal polyps or cancer when they do not. I am also concerned that some people who are found to have one or no MUTYH mutation could actually have MUTYH-Associated Polyposis because there are many other mutations in the MUTYH gene that are not included on the 23andMe test. Finally, as you have pointed out, this does not begin to address the most common inherited form of colorectal cancer (Lynch syndrome) or any of the other known hereditary colorectal polyp/cancer genes so individuals with these conditions might be falsely reassured into thinking that they are not at increased risk for colorectal cancer when they actually are.”

If you have a family history of colorectal cancer, you should talk to your health care provider about your risk and how this may affect your screening schedule.

Your health care provider may recommend speaking to a genetic counselor if you have a family history of colon, rectal, or other cancers in your family. This is why it is incredibly important to know your family health history! Dont rely only on 23andMe to check for colon cancer.

Why see a genetic counselor?

According to the National Society of Genetic Counselors, “genetic counselors have advanced training in medical genetics and counseling to guide and support patients seeking more information about how inherited diseases and conditions might affect them or their families, and to interpret test results."

A person who seeks genetic tests alongside a genetic counselor will not only have support, but they will have someone walk them through the process, test results, next steps, and even follow-ups. Follow-ups are important as new gene variants become discovered and may alter your current known risk of developing a disease.

Genetic counselors do the following:

  • Review and discuss your medical and family history
  • Discuss the likelihood that the cancer in your family could be due to an inherited gene mutation
  • Explore options for genetic testing
  • Explore the implications of a positive test result
  • Provide you with your personal risk for developing cancer if the testing is positive or negative
  • Review what the screening recommendations would be if the testing is positive or negative
  • Discuss the pros and cons of genetic testing
  • Help you understand if your health insurance will cover the test
  • Help you learn ways to manage your cancer risk
  • Discuss options to join genetic-related research studies, if appropriate

Most importantly, they can make sure you are getting the correct test that includes all of the genes and all of the mutations for which you are at-risk.

If you do decide to take the test, make sure to talk to your health care provider about the results and what they mean for you and remember that the results aren’t necessarily telling the whole story.

So what did I do and should I use 23andMe to check for colon cancer?

Direct to consumer testing is part of the landscape now, and many companies offer tests that are affordable. Often times, test results are collected and used in big data sets, so if you choose to move forward with one of these tests, it is important to learn about if and how your information will be used.

For example, if your test does come back as negative, this does not mean that you don’t have any chance of getting colorectal cancer. If the test comes back positive, it’s not one hundred percent that you will get cancer.

You can use the tests to gain more insight into your family history in general, but don't use them as a substitute for genetic counseling.

For more information:

Genetics Mini Magazine
Watch this webinar Genetic Testing and You
Prevent Cancer Statement

One thought on “23andMe and CRC Risk

  1. I was quite skeptical earlier but after reading your blog, I completely agree with your point on genetic counseling. I will share it definitely to one of my friend who has a cancer history. Keep it up.

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