Colorectal cancer is the third most common cancer in the United States and the second most common cause of cancer-related death. Routine screening for colon cancer could save up to 18,000 lives per year and significantly reduce the costs of cancer treatment. (Maciosek M, et al. Colorectal cancer screening: health impact and cost effectiveness. Am J Prev Med 2006;31(1):80-89)
Most colorectal cancers originate from adenomatous polyps; 30% of adults over the age of 50 develop such polyps, and these polyps become more common with increasing age. Polyps can be removed during colonscopy, thereby reducing the expected incidence of colorectal cancer. (Rickert R, et al. Adenomatous lesions of the large bowel: an autopsy survey. Cancer 1979;43(5):1847-57 and Winawer S, et al. Colorectal cancer screening: clinical guidelines and rationale. Gastroenterology 1997;112(2):594-642; 1997;112(3):1060; 1998;114(3):625)
Screening for colorectal cancer is recommended for average-risk individuals aged 50 years and older. Earlier or more intensive screening is required for persons at increased risk. An average-risk adult is one who is asymptomatic and who does not have a personal or family history of adenomatous polyps or any other illness that increases the risk for colorectal cancer (e.g., inflammatory bowel disease, familial polyposis, inheritable forms of colon cancer).
Public awareness campaigns have emphasized the importance of colorectal cancer screening, and opinions regarding the virtues of specific lifestyles that reduce individual risk are widespread. A summary of current evidence and recommendations follows.
Colorectal Cancer Screening Methods, Recommended Frequency, and Accuracy
- Colonoscopy: Although colonoscopy does not have a proven cancer mortality benefit, this screening method has the best single-test accuracy, and it is the final test that is performed to evaluate and treat people who exhibit abnormalities in other screening tests. Screening colonoscopy is recommended every 10 years for average-risk persons.
- Fecal occult blood testing (FOBT): Detection of blood in a person's stool prompts further testing to determine the source. A single FOBT performed in a doctor’s office will miss 95% of cancers; this method is not recommended for screening. Instead, patients should perform one test each day for three consecutive days at home (using cards obtained from their physicians). The cards are then returned to the doctor for analysis. FOBT screening should be performed annually if it is the sole screening modality.
- Flexible sigmoidoscopy: The majority of polyps and cancers typically occur in the lower reaches of the colon. Examination via flexible sigmoidoscopy every five years has been shown to reduce mortality from colorectal cancer. Current recommendations combine sigmoidoscopy every five years with FOBT every three years.
- Barium enema (BE): Prior to the advent of colonoscopy, this x-ray study was the primary means for detecting colonic polyps. When compared with colonoscopy, BE has a much lower detection rate; there is little evidence of mortality benefit using this modality.
- Newer methods: Fecal DNA testing, virtual colonoscopy (using CT), and Pillcam Colon are relatively new screening tests. While promising, these modalities have not generated sufficient data to determine their place in screening protocols. DNA testing appears to be more sensitive than FOBT for detecting invasive cancer and high-grade dysplasia (early cancer), but it isn’t particularly effective for detecting early polyps. Virtual colonoscopy, in its current form, is less accurate than colonoscopy for detecting small polyps, but it has fewer complications. Pillcam does not appear to be as sensitive or specific as colonoscopy, but it, too, has fewer complications. Colonoscopy, virtual colonoscopy, and Pillcam all require complete bowel preparation prior to the procedure.
Regardless of the screening method used, colorectal cancer screening is cost-effective and potentially life-saving.
(Adapted from Wilkins T, Reynolds P. Colorectal cancer: a summary of the evidence for screening and prevention. Am Fam Phys 2008;78(12):1385-92)
