Screening for Colorectal Cancer
January 30, 2002 3 minutes read
Screening for Colorectal Cancer
Abstract & Commentary
Synopsis: Many options exist for colorectal cancer screening, each with its own advantages and drawbacks. The best of these include fecal occult blood testing, sigmoidoscopy, and colonoscopy.
Source: Ransohoff DF, Sandler RS. N Engl J Med. 2002;346: 40-44.
Some of the considerations in selection of an approach to colorectal cancer screening include costs, safety, potential discomfort, and the individual patient’s fear of cancer.
Fecal occult blood testing of stool traditionally involves 3 serial samples, an approach tested in a number of randomized, controlled, clinical trials. However, at least 1 recent study also supported the use of a single test at the time of rectal examination. Occult blood tests probably should not be rehydrated since this increased false-positive rates. Some physicians recommend avoidance of aspirin, red meat, and horseradish prior to serial fecal occult blood testing. Colonoscopy is recommended if any occult blood test is positive since 17-46% of individuals with positive tests will have colorectal cancer or a large adenoma. Occult blood testing has been shown to reduce colorectal cancer deaths by 15-33% (similar numerically to mammography). Sigmoidoscopy is effective for finding lesions in the distal colon, and the risk of death from colorectal cancer can be reduced by 60% by the finding of a lesion within reach of the instrument, translating to a reduction of 30% for the colon as a whole. The exact reduction in risk of death from colorectal neoplasia afforded by colonoscopy is not known. However, it can be extrapolated to be much higher than either sigmoidoscopy or fecal occult blood testing. Colonoscopy does have a colon perforation rate of 2 per 1000 procedures vs. 1 per 10,000 for sigmoidoscopy. In the new millennium, there is little reason to consider barium enema as a suitable screening option for colorectal cancer due to low sensitivity for lesion detection. Virtual colonoscopy is still experimental and does not currently offer a meaningful alternative to colonoscopy.
Comment by Malcolm Robinson MD, FACP, FACG
All of the tests mentioned for colorectal cancer screening are considered to be cost effective—ie, they all cost less than $30,000 per year of life saved. For obvious reasons, gastroenterologists prefer colonoscopic screening. However, this is not yet verified as superior to the other 2 techniques in "competition." If sigmoidoscopy is done, the finding of an adenomatous polyp should trigger subsequent colonoscopy. At present, recommendations for a person with an average risk of colorectal cancer would be: annual fecal occult blood testing alone, sigmoidoscopy every 5 years, or a combination of the 2 tests. Colonoscopic screening, perhaps once every 10 years, is beginning to be offered as an option. In any case, whatever colorectal screening approach is selected, physicians should advise patients to reduce their risks of colorectal cancer by avoiding obesity and by limiting alcohol and red meat intake. Use of any of the available tests for colorectal cancer screening is clearly preferable to none.
Dr. Robinson, Medical Director, Oklahoma Foundation for Digestive Research; Clinical Professor of Medicine, University of Oklahoma College of Medicine, Oklahoma City, OK, is Associate Editor of Internal Medicine Alert.
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