Why you should consider clinical genetic testing for hereditary colon cancer
March 11, 2020
Public fascination with genetic testing has grown dramatically in recent years, with dozens of companies now offering to decode your DNA and provide insights into your ancestry and genetic health. In 2018, more than 12 million people said they participated in some form of genetic testing, according to the Centers for Disease Control and Protection (CDC).
The human genome, it seems, is having a moment.
However, the mainstream popularity of direct-to-consumer genetic testing – kits you can buy online or in the store – represents a double-edged sword for patients and health care providers. Commercial tests have increased access and awareness of inherited conditions, but they fall woefully short of giving patients a full or accurate picture of their own genetic health risks.
Consider colon cancer, for example, which is the second most deadly cancer in the United States. There are approximately 30 genes associated with hereditary colon cancer for which clinical testing is available at the moment. This translates to thousands of genetic mutations that can lead to a predisposition to developing colon cancer.
One particular direct-to-consumer (DTC) test that screens for hereditary colon cancer only looks for two common genetic variants in one gene linked to hereditary colon cancer – just a tiny snippet of your genetic information that tells us about your risk for developing colon cancer.
The bottom line is, interpreting genetic testing results can be quite complicated. While taking a DTC genetic test to learn about your ancestry or other traits may be an interesting exercise, it is important to understand that these tests are largely unregulated and should not be used to make decisions about your health care.
UT Southwestern’s Cancer Genetics program is one of the largest in the country. We counsel patients before and after a comprehensive DNA analysis using detailed medical and family history as a guide. If results show you are at increased risk for hereditary colon cancer, our genetic counselors can help create an early detection and screening plan, and discuss published guidelines regarding other risk-reducing options as indicated, including medications or surgical options.
Genetic testing results can also have important implications for your family members, and our team can help get your family appropriate medical care.
Detecting hereditary colon cancer
Only about 5% to 10% of colon cancers are hereditary, so before recommending genetic testing one of our 14 board-certified genetic counselors will do a complete risk assessment, looking for:
- A personal or family history of colon cancer
- Personal or family history of other types of cancer
- Multiple relatives diagnosed with colon cancer
- Relatives diagnosed with colon cancer before age 50
- Presence of 10 or more polyps shown on a colonoscopy
- Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC), is the most common hereditary cancer syndrome. As many as 1 in 300 people carry a genetic mutation associated with Lynch syndrome and have a significantly increased risk of developing colon cancer, as well as other cancers.
- FAP is characterized by more than 100 colorectal polyps in the colon. While it is less common – anywhere from 1 in 7,000 people to 1 in 22,000 have the condition, those with FAP have very high risks for develop colorectal cancer, at very young ages.
- Other genes: AXIN2, BMPR1A, CDH1, CHEK2, GREM1 MUTYH, NTHL1, POLD1, POLE, PTEN, SMAD4, STK11, and TP53
Colonoscopy remains the gold standard for identifying colon cancer, and national guidelines recommend starting colonoscopies between ages 45-50 for men and women at average risk for developing colorectal cancer.
For patients with a family history of colon cancer, screening should be started earlier – either at age 40 or 10 years prior to the earliest case of colon cancer in the family. Screening may also be performed more frequently.
For patients at increased risk for hereditary colon cancer, including genes implicated in Lynch syndrome (MLH1, MSH2, MSH6, PMS2, EPCAM) and polyposis genes (APC, MUTYH), the National Comprehensive Cancer Network (NCCN) continuously updates guidelines based on the latest research. Colonoscopies may begin as early as age 10 for patients with FAP.
Benefits and limitations of genetic testing
Ever since the mapping of the human genome in 2003, genetic testing has become a rapidly evolving science – one that energizes researchers and clinicians.
The benefits of clinical genetic testing are many:
- The test is easy: a simple saliva or blood test can unlock secrets and identify risks for inherited health conditions.
- The results can have a big impact on your health care: Knowing you are predisposed to colon cancer can save your life and reduce your risk for ever developing cancer. Results can also sometimes provide physicians with a roadmap for effective, precision cancer care. Comprehensive genetic testing can also alert family members to potential health risks.
- Results are private and protected: Many DTCs add your information to public databases, creating the potential for breaches in privacy. But the genetic testing conducted at UT Southwestern is protected health information and federal laws prevent employers and health insurance companies from discriminating based on the results. Our team of genetic counselors will discuss any exceptions that may apply to you.
- Access is improving: Most insurance companies cover some of the cost of clinical genetic testing and counseling, based on national guidelines. For those who do not have insurance, financial assistance programs can help with testing costs. Patient pay options have also become a bit more affordable now.
But like any fast-changing science, genetic testing has some limitations, too:
- Results don’t necessarily provide a “yes” or “no” answer: Our team of genetic counselors will consider your results, your medical history, and family history to guide your clinical care.
- DTC test results can be confusing: The majority of people are drawn to commercial tests because they’re convenient, but some DTC companies provide consumers with their raw genetic data, which can then be interpreted using third-party tools. Research shows that these unregulated tools often provide inaccurate information about disease risks that potentially could be used to make inappropriate medical management decisions by consumers.
- Tests may need to be updated: With advances in genetic testing technology and growing knowledge of hereditary colon cancer, if you had genetic testing before 2015, you might need to consider having update testing. Our team can discuss the most appropriate testing for you and your family.
The psychological impact of genetic testing is something we discuss with our patients as well. Some are eager to get results, but others are wary of finding out about a hereditary condition.
That’s one of the reasons our genetic counselors provide individualized risk assessments and use prediction models to determine if genetic testing is right for you.
Our genetics team sees more than 5,000 patients each year – more than most genetics and hereditary cancer programs in the country. While direct-to-consumer kits may satisfy a curiosity, genetic testing for hereditary cancers is not something we take lightly. Our focus is on helping you, whatever the results.