The U.S. Food and Drug Administration (FDA) Molecular and Clinical Genetics Panel of the Medical Devices Advisory Committee voted in late March to recommend that a new stool DNA (sDNA) test be approved for marketing as an option for colorectal cancer screening. Unlike other options such as colonoscopy, the current gold standard for colorectal cancer screening, the stool test is non-invasive and the sample can be collected at home with no need for bowel preparation or medication before it is mailed off for analysis.
Colorectal cancer is the third most common cancer and the third leading cause of cancer death among men and women in the U.S. As recently reported by the American Cancer Society, colorectal cancer rates have significantly dropped in the last ten years as a result of improved screening (see Colon Cancer Rates Decline, Highlighting Role of Screening). However, the availability of other reliable testing options like the sDNA test might boost screening rates further.
The FDA panel voted unanimously that the sDNA test is safe, effective, and has more benefits than risks. The FDA is expected to make its decision on whether to allow the test to be marketed in the next few months. The agency is not required to follow the recommendations of its advisory committees but frequently does.
The test works by testing a person's stool for altered (or signature) DNA that is shed from the digestive tract. Altered DNA occurs with colon cancers and precancerous polyps. The test also looks for the presence of blood in the stool sample, another possible indicator of colon cancer. The measurements for each marker included in the test are then incorporated into a mathematic algorithm and reported as a single value to indicate whether the test result is positive or negative for possible cancer. A positive screening result would be followed up with a colonoscopy, not just to confirm the results but also to remove any precancerous polyps found during the procedure.
The FDA advisory committee based much of its decision on a pivotal clinical trial published recently in the New England Journal of Medicine. The study included data from 10,000 patients at 90 sites in the U.S. and Canada. The study compared the sDNA test to the fecal immunochemical test for occult blood (FIT), already on the market, among people at average risk for colorectal cancer.
Sensitivity of the sDNA test (the test's ability to correctly identify individuals with cancer) was found to be 92% overall and 94% for early-stage cancers, which are the most curable, and "represents the highest sensitivity of any noninvasive test to date," according to study author Dr. Imperiale. In comparison, sensitivity of the FIT was found to be 74% overall.
However, the sDNA test was found to have a higher rate of false-positive results than did FIT (10-13% for sDNA compared to 4-5% for FIT) and concerns were raised regarding the complexity of the sDNA test. Technical problems with the test led to the exclusion of a larger number of participants in the sDNA group than the FIT group.
While the FDA advisory committee has voted to recommend approval of this sDNA test and it has shown improved performance in several aspects, more studies will be needed to evaluate how best this test should be used as part of a screening protocol.
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Tests: Fecal Occult Blood Test and Fecal Immunochemical Test
Conditions: Colon Cancer
Screening: Adults (30-49), Adults (50 and Up)
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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