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By Frederick H. Opper, MD, FACP, FACG, AGAF

Colorectal cancer (CRC) is the second leading cause of cancer deaths in men and women combined.  The incidence of both new cases and deaths has rapidly declined in the past 30 years due to increased screening and surveillance measures. The vast majority of CRC’s start out as benign polyps (growths). Some of these are destined to change over time (average 10 years) into cancer.  Because CRC is a deadly disease that usually has no symptoms in its early stages, the medical profession decided to pursue aggressive testing for colon cancer and colon polyps.

CRC screening usually starts at age 50. Several influential organizations including the American Cancer Society advocate for starting CRC screening at age 45. Subgroups at higher risk need to start even earlier. This article will discuss the commonly used methods for CRC screening.

Broadly speaking, CRC screening tests are either stool based or colonoscopy. These two strategies differ in cost, safety, effectiveness and availability.  Stool testing strategies for CRC are based on finding miniscule amounts of hidden blood that may indicate the presence of cancer or large polyps. They include annual FIT (fecal immunochemical testing) or annual high sensitivity guaiac testing.  A newer, highly advertised stool test, brand name Cologuard, combines a FIT test with a DNA test for mutations and is recommended every 3 years. I will focus on advantages and disadvantages of stool FIT testing and Cologuard as they are the most commonly used stool tests in the United States.   Of note, any positive (abnormal) stool screening test absolutely requires a colonoscopy to discern whether this actually indicates colon cancer or is a false positive.

 The FIT stool test is safe, inexpensive and convenient. Since large polyps are much more likely to turn cancerous than small ones, it is also important to know how often a given test will pick up large polyps. FIT is about 70% sensitive for cancer and about 30% sensitive for large polyps. This means that if you have a hidden cancer the FIT test will alert us 7 out of 10 times and will alert us 3 out of 10 times if you have a large polyp.

The Cologuard is also safe, available and convenient but expensive. It is 92% sensitive for CRC but only 42% sensitive for large polyps. Unfortunately, it has a 13% chance of a false positive triggering a colonoscopy. This colonoscopy (deemed a diagnostic colonoscopy by insurers) required for any positive stool test is often not as well covered by insurers as a screening colonoscopy, necessitating a higher out of pocket expense for patients.  The irony of insurers covering a colonoscopy simply for screening when we think nothing is wrong and not covering as completely for diagnostic colonoscopy when we suspect something is actually wrong, is quite another subject.  Cologuard is only recommended for patients at average risk for colon cancer. That is, any patient with a personal history of precancerous polyps, colon cancer, rectal bleeding or a family history of colon cancer or large precancerous polyps is not appropriate for Cologuard.

Colonoscopy every 10 years is considered the definitive test for CRC screening.  It directly examines the colon lining with the ability to remove abnormalities.   Its sensitivity for polyps far exceeds all other tests and for that reason it is considered the gold standard for CRC screening.  Screening colonoscopy is generally very well covered by insurers. It is relatively safe (though there is a rare risk of perforation).  There is a small bleeding risk if polyps are removed. The bowel prep (bowel cleanout) is absolutely necessary for a good exam although considered the most unpleasant aspect of the process by patients.  The sedation for the colonoscopy virtually assures a painless procedure.  Even with colonoscopy it is possible to miss a colon cancer or a large polyp.  However, colonoscopy affords us our best chance of finding these lesions.  Because precancerous polyps can actually be removed at colonoscopy it is considered to be our main tool for CRC prevention, whereas stool testing is considered to be a tool for CRC detection.

A primary care provider can help you to determine which CRC screening strategy is appropriate for you.  The only absolutely wrong course of action is to do nothing at all.

Frederick Henry Opper MD FACP FACG AGAF is Chairman, Department of Medicine Novant/NHRMC, and Clinical Associate Professor of Medicine UNC School of Medicine.  A graduate of Chicago School of Medicine, Dr. Opper completed Internship, Internal Medicine Residency and a Gastroenterology/Clinical Nutrition Fellowship at UNC-Chapel Hill.