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Update: non-invasive screening test for colon cancer: colonoscopy refined: these new findings may improve accuracy in detection and subsequent treatment of colon cancer; some experts disagree.

A new DNA-based test for colon cancer could transform colon cancer screening by enabling doctors to refer people for a colonoscopy (currently recommended for all those over 50) only if they test positive in the new test.

Unlike a colonoscopy, the DNA lest is noninvasive: It examines stool samples for the presence of four altered genes that are diagnostic of colon cancer. In trials, the test was able to detect 85.3 percent of colorectal cancers and 63.8 percent of polyps bigger than one centimeter (polyps this size are considered pre-cancers and most likely to progress to cancer). The new test was presented at the American Association for Cancer Research special conference on colorectal cancer, October 2010,

The test would be less expensive than a colonoscopy (about $300 compared to about $2,000 for colonoscopy) and potentially could boost compliance for colon cancer screening. "If widely used, and regularly, this test really does have the opportunity to eliminate colon cancer," says lead researcher David A. Ahlquist, MD, professor of medicine and a consultant in gastroenterology at the Mayo Clinic.

COLONOSCOPY PROCEDURE REFINED. While colonoscopy is effective in detecting cancers and advanced polyps in the lower (left) part of the colon and rectum, it's less successful in identifying them in the proximal (right) side or upper colon. Research presented at the American College of Gastroenterology annual meeting in October 2010 suggests that an endoscopic technique known as retroflexion, which involves angling the tip of the endoscope upwards in order to better visualize the proximal side of the colon, may aid in better identification. The proximal side of the colon involves the cecum, (through which the small intestine empties into the large intestine), the ascending colon, and the transverse colon).

Retroflexion isn't routinely performed because it raises the risk of discomfort to the patient and perforation of the colon. But in the study it was found to increase the diagnostic yield of polyps, including adenomas (benign tumors). The study, which included 1,000 patients, identified 500 polyps in 287 patients on forward examination (as the endoscope passed through) of the proximal colon, and an additional 68 polyps in 58 patients on retroflexion of the scope (once it was positioned in the proximal colon). "The risk of identifying a polyp on retroflexion was three times more likely among those who had a polyp detected on forward view compared to those patients who were negative on forward examination," says study leader Douglas K. Rex, MD, professor of medicine at Indiana University Medical Center.


COLONOSCOPY "MISS" RATE A CONCERN. Retroflexion was particularly effective in men, older patients and those with polyps found on forward examination. According to Dr. Rex, the technique typically takes less than a minute of extra time and is an opportunity to find polyps in an area where they are frequently missed. More important, 41 percent of the patients who had polyps identified via retroflexion had negative exams on forward examination. "Colonoscopy has a significant miss rate for the smallest adenomas, but retroflexion in the right side of the colon could reduce the miss rate associated with lesions on the proximal sides of the folds in the colon," says Dr. Rex.


JOANNE A.P.WILSON, MD, FACP, AGAF, Professor-Department of Medicine, Division of Gastroenterology, Duke


More Investigation Is Warranted

"The DNA-based test was developed to detect colon cancer and advanced polyps (large pre-cancers). In contrast, colonoscopy prevents colon cancer by removing smaller pre-cancers and removing or sampling more advanced lesions. This DNA test is not as sensitive as is needed for a screening test, missing about 15 percent of colon cancers and over 35 percent of the large advanced polyps. This study on the new colonoscopy procedure, retroflexion, highlights the need for careful examination of the right colon when performing screening colonoscopy. Retroflexion in the right colon may not be the optimal technique. A second forward view examination may be just as effective. Further investigation is warranted, and this preliminary report should not serve as an endorsement of this technique."
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Title Annotation:CANCER
Author:Wilson, Joanne A.P.
Publication:Duke Medicine Health News
Date:Jan 1, 2011
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