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Thursday, April 3, 2014

A new test for colon cancer

Worldwide, colorectal cancer is one of the most commonly diagnosed forms of cancer. In the U.S., it is the second leading cause of cancer-related deaths (behind only lung cancer), and kills about 50,000 people per year. Luckily, there is a screening test that can catch the disease early enough to treat it. Even better, that test could just get a whole lot less invasive.

The standard test for colon cancer is called colonoscopy. Not to put too fine a point on it, a long flexible tube containing a camera is passed through the anus into the large intestines. The entire colon is carefully examined for lesions or polyps, which are removed for biopsy. The test requires the complete emptying of the bowels prior to the procedure, which is generally agreed upon to be unpleasant.

Perhaps for this reason, nearly half of eligible patients avoid colon cancer screenings. Thanks to researchers from the Mayo Clinic, there may soon be an alternative. In partnership with Exact Sciences, the scientists have developed a new screening tool called Cologuard.

Cologuard tests stool samples for DNA changes associated with colon cancer. In the past, such tests were not sensitive enough to replace colonoscopy. However, new techniques in DNA detection and sequencing have made Cologuard a promising option.

The researchers recruited about 10,000 people between the ages of 50 and 84 for their study. Each person provided a stool sample (no cleansing, dieting, or medication required) and subsequently underwent colonoscopy (with the usual cleansing).

By colonoscopy, 65 patients were found to have cancer. The DNA testing Cologuard identified 60 of them. That’s a pretty good success rate, and certainly better than other noninvasive tests.

Obviously, there is room for improvement, especially if Cologuard is meant to completely replace colonoscopy. However, if you consider that this test might get many more people screened, Cologuard could be an extremely useful tool in an oncologist’s arsenal. 

Imperiale, T., Ransohoff, D., Itzkowitz, S., Levin, T., Lavin, P., Lidgard, G., Ahlquist, D., & Berger, B. (2014). Multitarget Stool DNA Testing for Colorectal-Cancer Screening New England Journal of Medicine DOI: 10.1056/NEJMoa1311194.

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