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Screening for Colon Cancer by Using a Computed Tomographic Scan Without a Laxative FREE

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The full report is titled “Diagnostic Accuracy of Laxative-Free Computed Tomographic Colonography for Detection of Adenomatous Polyps in Asymptomatic Adults. A Prospective Evaluation.” It is in the 15 May 2012 issue of Annals of Internal Medicine (volume 156, pages 692-702). The authors are M.E. Zalis, M.A. Blake, W. Cai, P.F. Hahn, E.F. Halpern, I.G. Kazam, M. Keroack, C. Magee, J.J. Näppi, R. Perez-Johnston, J.R. Saltzman, A. Vij, J. Yee, and H. Yoshida.

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Ann Intern Med. 2012;156(10):I-36. doi:10.7326/0003-4819-156-10-201205150-00002
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What is the problem and what is known about it so far?

Many deaths from colon cancer can be prevented by detecting the cancer early or by detecting suspicious precancerous lesions. This is usually done by screening for early cancer or its precursor with colonoscopy. Colonoscopy involves the insertion of a flexible fiberoptic scope through the anus so that the colon can be inspected and biopsy specimens of suspicious lesions can be obtained. An alternative is to have a computed tomographic x-ray study (CT scan) to see whether there are suspicious lesions that require colonoscopy. Both studies require cleansing of the bowel with laxatives (usually beginning 1 to 2 days before the study) to remove feces that would interfere with seeing suspicious lesions during the study. The need to prepare for the study with a laxative is a barrier to many patients and the reason that many people do not complete recommended colon cancer screening.

Why did the researchers do this particular study?

To see whether a new technique involving a CT scan that does not require a laxative preparation can successfully identify suspicious lesions.

Who was studied?

605 adults at moderate risk for colon cancer.

How was the study done?

Beginning 2 days before the laxative-free CT scan, patients ate a low-fiber diet that included a special material to “tag” their feces. After the CT scan was done, a computer program removed the feces from the pictures to allow a radiologist to look for suspicious lesions. Up to a few weeks later, each patient had a standard colonoscopy with the standard laxative preparation to remove feces. The results of the 2 studies were compared. The researchers also asked patients about their experiences with the tests.

What did the researchers find?

The laxative-free CT scan was nearly as good as colonoscopy at detecting larger lesions (the ones most likely to become cancerous) but not as good at detecting smaller suspicious lesions. The patients reported less discomfort or difficulty preparing for the laxative-free CT scan than for the colonoscopy that required a laxative.

What were the limitations of the study?

The study was performed at highly specialized centers with a small group of radiologists experienced in reading these types of CT scans. This experimental technique requires additional study before it can be recommended for general use.

What are the implications of the study?

If other studies and settings confirm these findings, laxative-free CT scanning may be a reasonable alternative to standard colonoscopy as the initial step in screening for colon cancer in some patients.





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