The availability of a simple non-invasive test capable of detecting colorectal cancer specific products with reasonable sensitivity and specificity might avoid the invasiveness, unpleasant bowel preparation, and risk of bleeding and perforation related to colonoscopy. Molecular marker combinations in faecal DNA testing have been shown to produce high rates of both colorectal cancer and advanced adenoma detection in selected patient populations,1 and observations from large representative groups are emerging.
Imperiale and colleagues2 have recently reported the results of the first large study of faecal DNA testing in asymptomatic subjects. A total of 4404 average risk adults, who were at least 50 years old, underwent faecal occult blood testing, faecal DNA testing, and colonoscopy, which was considered the reference standard. Comparing test results in a random subgroup of 2507 persons, the authors found that the faecal DNA test was much more sensitive than faecal occult blood testing in detecting colorectal cancer and adenomas with high grade dysplasia. However, the sensitivity for both the faecal DNA panel and faecal occult blood testing was low. In particular, the faecal DNA test detected only 52% of colorectal cancers and 15% of adenomas, rates that were far lower than those previously reported in the literature for multitarget testing.3–5 Furthermore, in the same study,2 the sensitivity of faecal occult blood testing (13%) was unexpectedly low.
Interestingly, in the results section, Imperiale and colleagues2 reported that “among 1423 subjects with negative findings on colonoscopy, 79 had a positive faecal DNA panel and 68 had a positive Hemoccult II test, for specificities of 94.4% and 95.2%, respectively”. The question immediately arises as to whether these patients subsequently developed “advanced neoplasia” or minor polyps and consequently whether the results from the DNA stool test or faecal occult blood test were falsely or truly positive. In fact, colonoscopy could have produced false negative results for several reasons, including misinterpretation of what was visualised or failure to perform adequate biopsy of the lesions seen.6 In this case, it could be intriguing to compare the ability of faecal DNA panel versus that of the Hemoccult II test in predicting the early occurrence of “advanced neoplasia” when colonoscopy misses the disease.
Conflict of interest: None declared.
References
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