Colon cancer screening
is the cologuard stool DNA test right for me?
by Jamal Ross
Having a realization that colon cancer is a serious disease that is largely preventable is half the battle. Once you make the commitment to be tested for colon cancer, there is another challenge to determine which test is best for you. As we continue our discussion of colon cancer tests, we will take a closer look at a test that can pick up cancer DNA in your stool. This is called a multitarget stool DNA test, but it is also known as Cologuard, which is the trade name.
The Cologuard test measures cancer DNA our stool by detecting a cancer protein called KRAS. There are other cancer proteins picked up by the Cologuard as well. This test can be performed at home, which can be seen as convenient. Yet, the Cologuard test requires a larger stool sample to be accurate in order to ensure enough cancer DNA is collected. The home testing kit comes with a bucket to collect a full stool sample and preservative to mix with your sample. The idea of collecting a larger stool sample may deter some, but there is no need to restrict your diet, take special medications or laxatives before completing this test. The Cologuard test can be done every 3 years. The Cologuard kit also contains a FIT card for you stool as well. The Cologuard test requires a prescription from you doctor. The sample needs to mailed off 72 hours after you collect your stool sample. (1) If your Cologuard test is positive, it is recommended that you receive a colonoscopy.
The Cologuard test can pick up 94% of colon cancers. (2,3) Yet, similar to the FIT, large and small pre-cancerous masses, or adenomas, are missed. Also, while the Cologuard picks up a lot of cancers, some can have a positive Cologuard test when in actuality no cancer is present. This is called a false positive result. We do not like tests that have a lot of false positive results. This leads to less accuracy and anxiety for those who end up not having cancer.
Here is the bottom line: the Cologuard test is a newer option for colon cancer screening. Unlike the FIT, Cologuard detects cancer directly. We know the test can be done every 3 years, but there is no universal agreement on this timing. While the test can be done at home, the idea of collecting and manipulating a larger sample of stool can be off-putting. While the test picks up a large number of colon cancers, it also has a problem with a number of false positive readings. All positive results need a colonoscopy. Which begs the question: Should I just start with a colonoscopy? As a result, the Cologuard test has not caught-on in the medical community and a colonoscopy remains the gold standard to detecting colon cancer.
Colon Cancer Series
1. Doubeni C. Tests for screening for colorectal cancer. In: UpToDate, Elmore J & Lamont JT. (Eds), UpToDate, Waltham, MA. (Accessed on July 24, 2021)
2. Zauber A, Knudsen A, Rutter CM, et al. Evaluating the Benefits and Harms of Colorectal Cancer Screening Strategies: A Collaborative Modeling Approach. AHRQ Publication No. 14-05203-EF-2. Rockville, MD: Agency for Healthcare Research and Quality; October 2015.
3. Knudsen AB, Zauber AG, Rutter CM, et al. Estimation of Benefits, Burden, and Harms of Colorectal Cancer Screening Strategies: Modeling Study for the US Preventive Services Task Force. JAMA 2016; 315:2595.