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Cologuard: A Detailed Review

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    In August of 2014, the FDA approved Cologuard the first colorectal screening test that uses DNA to identify cancer cells in a patient’s stool sample. The company responsible for the invention of Cologuard is Exact Sciences, a multimillion dollar research and development conglomerate that specializes in at-home cancer screening tests. Since its release into the medical community, approximately 3.5 million people have used Cologuard to screen for colorectal cancer. In 2019, Exact Sciences labs processed 1.69 million Cologuard tests while touting its 92% sensitivity and 87% specificity rates for detecting colorectal cancer as selling points. 

    Cologuard, also known as a multitarget DNA stool test,  is a non-invasive colon cancer screening test that is done in the privacy of your home and mailed to a lab for analysis You are eligible for Cologuard if you are at an average risk for colorectal cancer with no family or personal history of colon cancer.

    Overview

    Cologuard, also known as a multitarget DNA stool test,  is a non-invasive colon cancer screening test that is done in the privacy of your home and mailed to a lab for analysis You are eligible for Cologuard if you are at an average risk for colorectal cancer with no family or personal history of colon cancer. The test detects mutations in the colon cells that shed from the intestinal lining into the feces. Cologuard also detects microscopic amounts of blood in the stool, so it serves as a dual screening for both mutated cells shed by cancerous tumors and bleeding polyps. A positive result from a Cologuard screening is generally followed by a colonoscopy to rule out colorectal cancer and to remove any polyps that may be found during the visual exploration of the colon. very small polyps and the precancerous adenomas. Important performance findings of Cologuard tests include:

    • Cologuard: Has a 92.3% sensitivity for detecting colon cancer at all stages 
    • Cologuard: 94% of early stage colon cancers are sensitive to the Cologuard test
    • Cologuard: Has a specificity of 95% for ruling out the presence of polyps and colon cancer

    Cologuard is highly sensitive due to its ability to identify cancerous cells using DNA-detecting technology. Because of these accurate ratings, Cologuard tests can be repeated every three years in average risk patients. Keep in mind that if you test positive in any of the home screening tests, you will need a colonoscopy to locate the source of the bleed and get any associated polyps removed. If there are any polyps found or abnormal tissue growths (adenomas), you may not be eligible for home screenings from that point on. 

    Cologuard or multitarget DNA test has a high sensitivity for detecting colorectal cancer without the need for bowel preparation are dietary restrictions

    Cologuard: A Combination of Two Tests

    FIT-DNA

    The Cologuard screening test is a combination of two tests, the fecal immunochemical test (FIT)  and a DNA screening for abnormal cancer cells. The lining of the colon sheds cells routinely throughout the day and these cells end up in the feces, or stool. This shedding allows the intestinal lining to renew and maintain its healthy tissue for optimal health. Abnormal cells from a polyp or tumor will also shed into the feces along with any occult blood caused by broken blood vessels.

    The Cologuard home colon cancer screening test detects cancer by identifying DNA markers from abnormal cells and occult blood in stool samples. A cancerous tumor in the colon will contain mutated DNA fragments that can be detected with special lab tests like the FIT- DNA test or Cologuard. Lab pathologists test the  stool samples sent in by patients for increased levels of mutated DNA biomarkers that are found in shedded colon cells. The test detects mutations in the following genes:

    • KRAS
    • NDRG4
    • BMP3
    • B-Actin

    These biomarkers indicate the presence of colorectal cancer or precancerous tumors known as adenomas. 

    Stool samples are also tested for the presence of a protein found in blood using the antibody test, fecal immunochemical test (FIT).  The test specifically tests for hemoglobin, the iron-containing protein that carries the oxygen in the blood cell. A polyp is an abnormal growth of tissue that often will bleed due to tiny broken blood vessels caused by the stool passing through the colon. The test is highly sensitive to microscopic amounts of blood caused by these bleeding polyps. 

    How The Cologuard Test Works

    The Cologuard home colon cancer screening test detects cancer by identifying DNA markers and occult blood in stool samples. You are not required to change your diet or medications before this test. Once you collect a sample of your stool, you will send or drop off your sample to a lab. The lab will return the results to your physician or healthcare provider who will contact you as soon as they arrive. 

    Opening & Using The Kit

    Each Cologuard kit contains the following:

    • Patient guide instructions and how to return your kit pamphlet
    • 1 bottle of liquid preservative
    • 1 sample container
    • 1 tube (contains liquid solution)
    • 1 bracket
    • 1 Shipping box

    Once you collect your sample, you simply mail the sample in according to the directions that are in the kit. You can also store your kit before you are ready to use it in a cool, dry place until you are ready to take the test. Keep the kit out of the reach of children and away from direct sunlight and heat. Your sample needs to be tested soon after you collect it so choose a day that is not a holiday or weekend to take the test. 

    Lab results

    Generally, there are three results given:

    Positive result. This indicated that the test detected blood in the stool or abnormal DNA in the colon lining cells shed in the sample. A positive finding could mean that there are precancerous or cancerous cells found in the sample. Some positive cases are the result of a false positive, which means there is no cancer or precancer present. All positive results are typically followed up by a colonoscopy. 

    Negative result. A negative result indicates that there was no abnormal DNA or stool detected in the stool sample. One should be aware, however, that this can be caused by a false negative result, which means cancer or precancerous cells are present but were not detected. Talk to your healthcare provider if you want further testing or have any questions about the results. 

    No result obtained. In this case, the lab was unable to produce a result from the sample that was provided. You may need to repeat the test. Ask your physician to see what the next steps hold. 

    Like all stool tests, you will be asked to collect a stool sample during a regular bowel movement. There are no dietary or medication restrictions you need to follow before collecting your sample. The testing kit usually contains labels, a sample container, a tube, preserving liquid, and instructions for you to follow. Once you collect your sample, you will ship it to the lab within 24 hours.

    Pros and Cons

    Colorectal cancer is a quiet cancer where symptoms of the disease typically show up when the disease is in its advanced stages. Colorectal cancer screenings, like colonoscopies, detect cancer early and help to stop the metastasis of the disease by catching it before it spreads. A colonoscopy is considered the gold standard for detecting colorectal cancer by physicians and health professionals alike.

    Many people are more willing to test for colorectal cancer using an at-home screening test that is non-invasive and does not require a bowel preparation. Cologuard is often prescribed by a physician as an alternative to a colonoscopy due to the test’s high level of accuracy in detecting cancer and ability to detect larger sized polyps. 

    However, 40% of all people over the age of 50 who are advised to get screened for colorectal cancer do not get screened for several reasons, including not wanting to undergo an invasive colonoscopy procedure. Many people are more willing to test for colorectal cancer using an at-home screening test that is non-invasive and does not require a bowel preparation. Cologuard is often prescribed by a physician as an alternative to a colonoscopy due to the test’s high level of accuracy in detecting cancer and ability to detect larger sized polyps. 

    Pros

    • Detects 92% of colorectal cancers
    • Non-invasive
    • Inexpensive compared to a colonoscopy
    • Typically covered by most insurances
    • Covered by Medicare
    • Convenient
    • Requires no bowel preparation
    • Serves populations in remote areas with limited access to medical facilities

    Cons

    • Detects 42% of advanced polyps
    • More expensive than other at home colon cancer screening test ($600)
    • 13% of tests are returned with a false positive
    • Not accurate in finding large polyps
    • Still requires a colonoscopy for any positive findings (even false positives)
    • A colonoscopy followed by a Cologuard positive result is considered diagnostic and many patients’ insurance will not cover diagnostic colonoscopies
    • Typically required every 3 years, whereas a colonoscopy is every 5-10 years

    References

    Imperiale, T. F., et., al. (2014, April 03). Multitarget stool DNA testing for colorectal-cancer screening. New England Journal of Medicine, 370, 1287-1297. Retrieved from NEJM: https://www.nejm.org/doi/full/10.1056/nejmoa1311194

    Mayo Clinic Staff. (2014, December 03). Cologuard primed to change landscape of CRC screening. Retrieved from Mayo Clinic: https://www.mayoclinic.org/medical-professionals/digestive-diseases/news/cologuard-primed-to-change-landscape-of-crc-screening

    Mayo Clinic Staff. (2015, October 30). Mayo Clinic: Cologuard stool DNA test accurate for screening for colorectal cancer in Alaska Native People. Retrieve from Newswise: https://www.newswise.com/articles/mayo-clinic-cologuard-stool-dna-test-accurate-in-screening-for-colorectal-cancer-in-alaska-native-people?sc=mwhn

    Lieberman, D., et., al. (2016, November). Screening for colorctal cancer and evolving issues for physicians and patients. JAMA, 316(20), 2135-2145. Retrieved from JAMA Network: https://jamanetwork.com/journals/jama/article-abstract/2585984

    Oliver, E. (2020, April 09). 4 gastroenteroligists share their thought on Exact Sciences’ Cologuard. Retrieved from Becker’s GI & Endoscopy: https://www.beckersasc.com/gastroenterology-and-endoscopy/4-gastroenterologists-share-their-thoughts-on-exact-sciences-cologuard-2.html

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