Colon Cancer Screening: What Are the Options?

Colon cancer is currently one of the most common cancers in the United States, superseded only by breast, lung, and prostate cancer. (1) Screening is crucial for helping doctors detect colon cancer in its early stages, when it is more treatable. However, there is significant controversy over what constitutes the best colon cancer screening method, and research shows that doctors are failing to provide their patients with balanced information about all the screening options, thus preventing patients from making informed decisions. (2) Read on to learn about the pros and cons of the available colon cancer screening methods and how you can help your patients determine the best screening type for their unique needs.

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Current Colon Cancer Screening Methods

The purpose of colon cancer screening is to detect early-stage colon cancer and precancerous lesions in asymptomatic people before cancer develops or when it is still highly treatable. (3) The U.S. Preventive Services Task Force (USPSTF), a panel of national experts in disease prevention and evidence-based medicine, recommends that people at average risk for colon cancer commence screening at 50 years of age. Screening should continue until age 75, after which patients and their healthcare providers can decide whether to continue screening based on factors such as life expectancy, health status, and prior screening results. (4) The USPSTF endorses multiple methods for colon cancer screening. These methods include colonoscopy, the high-sensitivity fecal occult blood test (FOBT)/fecal immunohistochemical test (FIT), the stool DNA test, flexible sigmoidoscopy, and CT colonography.

Colonoscopy

Colonoscopy is an endoscopic examination of the large intestine in which a long, flexible scope is inserted through the anus into the rectum and colon, where it is used to capture images of the entire lining of the colon. If abnormal growths are seen during the procedure, the doctor can take a biopsy or snip off the growths using a tool attached to the endoscope. It is recommended that this procedure be performed every 10 years.

High-Sensitivity Fecal Occult Blood Test and Fecal Immunohistochemical Test (FIT)

Both polyps, which are abnormal growths of tissue projecting from the colon wall, and colon cancers can bleed; FOBT and FIT detect tiny amounts of blood in the stool and can indicate the presence of precancerous or cancerous lesions. This test requires a stool sample and is performed annually.

Colonoscopy is not the only option for #coloncancer screening. Gut microbial analysis may be the future.

Stool DNA test

Like FOBT and FIT, the stool DNA test detects tiny amounts of blood in stool that may signify cancerous lesions; however, it also detects 21 genetic mutations associated with the pathogenesis of colon cancer. When used as a sole source of screening, it is recommended that this test is performed every three years.

Flexible Sigmoidoscopy

As with colonoscopy, flexible sigmoidoscopy involves the insertion of an endoscope through the anus into the rectum and colon. However, it only visualizes the left side of the large intestine, the sigmoid colon, rather than the entire colon. When used as the sole testing modality, flexible sigmoidoscopy should be performed every five years.

CT Colonography

CT colonography, also referred to as “virtual colonoscopy,” uses x-ray equipment to obtain a series of pictures of the colon. A computer then assembles the pictures into a detailed image of the entire colon.

The Pros and Cons of Colon Cancer Screening Methods

Even though it is not the only way to screen for colon cancer, colonoscopy has become the default screening test ordered by many physicians. Concerningly, research indicates that doctors are failing to provide their patients with balanced information about the full range of screening methods available. In an observational study of audiotaped clinic visits between patients and their providers, it was found that doctors failed to discuss critical aspects of colon cancer screening, such as the pros and cons of all available screening methods, with their patients. (5) As healthcare providers, we need to inform our patients about the different types of colon cancer screening, not just colonoscopy, so that they can make informed decisions about screening and take charge of their own health. 

Colonoscopy

Pros

• Colonoscopy visualizes the inner lining of the entire colon.
• A biopsy can be performed if abnormal growths are detected.

Cons

• Full cleansing of the colon is required.
• Diet and medications need to be adjusted before the test.
• Sedation is needed during the procedure.
• Colonoscopy may not detect small polyps or flat lesions and cancers.
• Colonoscopy is expensive—the average colonoscopy cost is $3,081—for those with insurance plans that do not cover the cost of screening. For those with plans that cover colonoscopy, deductibles range from zero to over $1,000. (6) While the Affordable Care Act requires coverage of colon cancer screening tests, plans that started before September 23, 2010, may have varying coverage requirements. (7)
• Endoscopes are not single-use or disposable; they are used repeatedly. Bacteria form biofilms on endoscopes, increasing the potential for cross-contamination of fecal matter and tissue. (8)
• Colonoscopies lead to “serious medical complications,” including colonic perforation and bleeding, in five out of every 1,000 patients. (9)
• Doctors receive financial kickbacks for referring patients for colonoscopies. This may bias their decision to inform their patients about other colon cancer screening methods.

FOBT and FIT

Pros

• No cleansing of the colon or dietary restrictions are required prior to the test.
• FOBT and FIT are non-invasive. The tests only require a stool sample, which can be collected at home and poses no risk of damage to the colon.
• FOBT and FIT are inexpensive. The cost of the test ranges from $3 to $40. (10)
• Multiple randomized, controlled clinical trials have found that annual and biennial FOBT screening significantly reduces the incidence and rate of death from colorectal cancer. (11, 12, 13) The reduction in incidence and mortality is the result of earlier detection and surgical removal of malignant colorectal tumors and premalignant adenomatous polyps.

Cons

• False-positive results are possible with both FOBT and FIT.
• The sensitivity of FOBT is higher for larger polyps, which are more likely to bleed, so it may miss smaller polyps. (14)

Stool DNA Test

Pros

• In adults at average risk for colon cancer, the stool DNA test was found to be more sensitive than the FIT test. (15)
• No cleansing of the colon or dietary restrictions are required.
• The stool sample can be collected at home and there is no risk of damage to the colon.
• The stool DNA test is lower in cost than colonoscopy. The cost ranges from $400 to $800.

Cons

• The stool DNA test is higher in cost than FOBT/FIT.
• Sensitivity for adenomas is low.
• False-positive results are possible.

Sigmoidoscopy

Pros

• Minimal cleansing of the colon is required.
• When performed just once between the ages of 55 and 64, flexible sigmoidoscopy significantly reduces the incidence and mortality from colorectal cancer. (16)
• Complications are rare.
• A biopsy can be performed if abnormalities are detected during the procedure.

Cons

• Medication and diet changes may be needed before the test.
• Sigmoidoscopy can’t detect problems in the upper portion of the colon.
• The test is invasive and there is a small risk of bleeding, perforation, or tear of the colon.

CT Colonography

Pros

• CT colonoscopy is less invasive than a standard colonoscopy.
• No sedation is required.

Cons

• The test exposes the body to ionizing radiation, which is an established cause of cancer. (17)
• It requires a thorough bowel prep, equivalent to that needed for standard colonoscopy.
• CT colonography carries a small risk of bowel perforation because a small tube must be inserted into the rectum to inflate it with air before x-ray images are taken.
• CT colonography may miss up to 10 percent of large colorectal adenomas and cancers (lesions greater than or equal to 10 millimeters in diameter). The sensitivity of CT colonography is even lower for lesions smaller than 10 millimeters in diameter. (18)
• If a lesion is seen, standard colonoscopy is still required. Approximately 8 percent of patients end up having to go through both CT colonography and standard colonoscopy. (19)

When guiding your patient through the decision-making process, these are some factors that should be considered: (20)  

• The patient’s age, medical history, family history, and general health
• Potential harms of the test
• Preparation required for the test
• Whether sedation is needed
• Follow-up care
• Convenience of test
• The cost of the test and whether it is covered by insurance

Bacteria: The Future of Colon Cancer Screening?

Fascinating new research indicates that gut bacteria may play a pivotal role in the development of colon cancer. Scientists have found that two types of bacteria commonly found in the gut, Bacteroides fragilis and E. coli, can penetrate the protective mucus shield lining the colon, colonize the intestinal lining, and release toxins that provoke DNA damage and oxidative stress. The inflammatory environment created by these bacteria thus supports the growth of tumors. (21) Another type of gut bacteria, Fusobacterium nucleatum, has also been implicated in the development of colon cancer and has even been found in colon tumors. (22) These findings are significant because they indicate that gut microbial analysis may be a valuable screening tool in the future for assessing the risk of colon cancer. If microbes associated with colon cancer are detected in such an analysis, more frequent screening and the implementation of other preventive measures, such as dietary changes and balancing of the gut microbiome, may be warranted to reduce the risk of colon cancer.