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Press Release
Fecal Blood Test Misses Majority of Colon Cancers and Serious Precancerous Colon Growths
Release 5 p.m. ET August 22, 2001
U.S. Department of Veterans Affairs researchers have found that one-time administration of widely used screening mechanisms misses significant percentages of serious precancerous growths in people with no symptoms of colon cancer. Reporting in the August 23 issue of the New England Journal of Medicine, VA scientists say effective screening programs for colon cancer require repeat testing.
The researchers, led by David Lieberman, M.D., of the Portland VA Medical Center, found that one-time screening with a fecal occult-blood test, the most commonly used screening test for colon cancer, detected less than 25 percent of serious precancerous colon growths in people with no symptoms. A one-time sigmoidoscopy, another common screening technique, detected 70 percent, and combined one-time testing found 76 percent-still missing almost a quarter of the precancerous growths.
"We want to emphasize that people who have these screenings need to go back at intervals for repeat testing," said Dr. Lieberman, chief of gastroenterology and professor of medicine at the Portland VA Medical Center and Oregon Health & Science University. For average-risk individuals age 50 and over, recommendations of the U.S. Preventive Services Task Force call for a yearly fecal occult-blood test (FOBT) and sigmoidoscopy every five years for colon cancer screening.
"But what happens in real life is that patients often get only one test and no follow-up," Lieberman said. "This study tells us physicians can't use that single negative test to reassure our patients and that people need to return for repeat testing in order for screening programs to be effective." Several studies have shown lower rates of deaths from colon cancer in patients who receive routine testing with FOBT or sigmoidoscopy, he noted.
Supported by the VA Office of Research and Development's Cooperative Studies Program, Lieberman and his colleagues studied 3,121 apparently healthy volunteers aged 50-75 at 13 VA medical centers around the country. All study participants underwent colonoscopy, the only procedure that allows physicians to search the entire colon for cancer or precancerous growths, to determine the effectiveness of colorectal cancer screening with FOBT and sigmoidoscopy in people with no symptoms. Nearly 2,900 subjects returned samples for the FOBT, which examines a fecal smear for traces of blood shed by a tumor. This is the largest study assessing the FOBT in which patients also had colonoscopy to detect cancers the blood test alone was missing.
During colonoscopy, a flexible lighted hollow tube about the width of a finger is inserted through the rectum into the colon. The colonoscope is connected to a video camera that reveals the colon's lining. Because all study patients underwent colonoscopy, the researchers were able to compare its effectiveness to that of sigmoidoscopy, a similar but more limited technique that uses a shorter tube reaching only the lower or "distal" part of the colon.
The team also found that a single FOBT, sigmoidoscopy or combination of the tests was less likely to detect serious precancerous growths as subjects aged. People 60 or older are more likely than those aged 50-60 to develop cancers in the upper colon, where they cannot be detected by sigmoidoscopy, Lieberman noted.
In a previous study of the 3,121 patients, the VA researchers found that sigmoidoscopy missed at least a third of colon cancers or serious precancerous growths (New England Journal of Medicine, July 20, 2000). Although colonoscopy is more complicated to perform and much more expensive than sigmoidoscopy, Lieberman said, a case certainly can be made for colonoscopy as a primary screening tool in men--or for routine FOBT and/or sigmoidoscopy in men aged 50-60, followed by a colonoscopy at age 60. Because colonoscopy detects lesions long before they develop into cancer, no further screening would be needed in the decade following the procedure. Further, if serious precancerous growths are detected and removed, many cancers can be prevented.
Lieberman cautioned that 97 percent of study patients were male, and noted that women develop precancerous lesions and cancer in the colon an average of 5-7 years later in life than men. Additional research is needed, he emphasized, to look at screening effectiveness specifically in women.
Co-authors of the new report include David G. Weiss, Ph.D., and other investigators of the VA Cooperative Study #380 Group.
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