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Colorectal Cancer Tests Are Not Created Equal

WebMD Health News
Reviewed by Gary D. Vogin, MD

Aug. 22, 2001 -- Colorectal cancers kill more Americans each year than any malignancy except lung cancer, and a large number of those deaths could be prevented with better screening. But a new study offers more evidence that the most widely used screening methods are not created equal.

The study, reported Aug. 28 in TheNew England Journal of Medicine, found two of the most common screening methods for precancerous growths in the colon were often ineffective. For instance, one-time screening with the least invasive and most commonly used technique called fecal occult blood testing, a chemical test to detect blood that is visually undetectable in the stool, missed precancerous polyps in almost three out of four people.

Furthermore, one-time screening combining the fecal test with flexible sigmoidoscopy, which involves the insertion of a hollow, lighted tube to inspect the wall of the rectum and part of the colon, still missed the polyps in about one-fourth of patients. Sigmoidoscopy allows doctors to look for the precancerous growths only in the lower half of the colon.

Researcher David A. Lieberman, MD, and colleagues concluded that screening programs combining fecal occult-blood testing, or FOBT, and sigmoidoscopy need to be repeated at appropriate intervals to be most effective. Their findings add to the evidence that a more invasive procedure known as colonoscopy, which allows doctors to look for precancerous growths throughout the entire colon, is the best available colorectal cancer screening method.

"This research will help physicians counsel patients on the available colorectal cancer detection methods," Lieberman tells WebMD. "We now know that serious growths will be missed in about a fourth of patients who receive one-time fecal occult testing with sigmoidoscopy. That is something patients need to know when they decide which procedure to have." Lieberman heads the gastroenterology department at Oregon Health Sciences University in Portland.

Regular colorectal cancer screenings are recommended for those who are 50 and over, but the CDC estimates that fewer than half of those who should be are being screened.

Colonoscopy is widely recognized as the most accurate test available, but it is also the most invasive and it requires sedation. It is also expensive, costing from around $1,000 to more than $3,000 in the U.S. Still, colonoscopy allows doctors to remove polyps that might otherwise become cancerous and if either FOBT or sigmoidoscopy revealed a problem, colonoscopy would need to be done anyways.

Lieberman says that FOBT and sigmoidoscopy, while not perfect, have a place in colorectal cancer screening. Many health organizations still recommend annual fecal occult testing, as well as a sigmoidoscopy every five years or a colonoscopy every 10 years for those 50 and over.

"This research shows that physicians can't really sit down with patients who have had a single FOBT and sigmoidoscopy and tell them they have nothing to worry about, because a quarter of those patients could still have something serious that hasn't been spotted," Lieberman says. "With colonoscopy they can offer patients that reassurance, assuming the exam is done correctly."

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