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BMJ 2008; 337 doi: (Published 13 October 2008) Cite this as: BMJ 2008;337:a2061

Stool DNA test for colorectal tumours looks promising

Colonoscopy is currently the best way to find colorectal cancers and precancerous adenomas in asymptomatic individuals. Not everyone wants to go through a colonoscopy, however, so scientists are currently refining less invasive options such as testing stool samples for genetic material shed from tumours in the gut. One DNA test looked more useful than tests for occult blood in a recent study, although colonoscopy would still be needed for people who test positive.

The second generation DNA test had a sensitivity of 40% (95% CI 32% to 49%) for detecting curable cancers, adenomas more than 1 cm in diameter, and dysplastic adenomas, compared with 11% (6% to 16%) for Hemoccult and 21% (15% to 27%) for HemoccultSensa. The authors studied stool samples from more than 4000 adults at average risk. A first generation DNA test performed badly in the same study, with a sensitivity no better than occult blood tests.

Low sensitivities and high numbers of false positives suggest that the technology still has some way to go, says an editorial (p 509), although the theory behind the tests is sound. Adenomas bleed intermittently but shed continuously, so looking for cells and the genetic material inside them makes good sense. The ultimate goal is to develop a sensitive molecular test for mutations that happen early along the road from adenoma to invasive cancer, says the editorial. The best test in this study looked for three genes, two of which mutate at the precancerous stage.

The latest US guidelines (Ann Intern Med 2008, published on the same day as this study, still recommend sigmoidoscopy, colonoscopy, or high sensitivity faecal occult blood testing for adults aged between 50 and 75. The US Preventive Services Task Force does not recommend routine screening for anyone over 75.

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