Ahlquist DA et al. (2008) Stool DNA and occult blood testing for screen detection of colorectal neoplasia. Ann Intern Med 149: 441–450

Fecal occult blood testing (FOBT) has been proposed as an alternative to colonoscopic screening for the detection of colorectal cancer, but requires multiple stool samples because occult bleeding is intermittent. By contrast, DNA markers from potentially cancerous cells are thought to be shed continuously. Thus stool DNA testing requires just one sample and offers an alternative, simple and noninvasive approach to screening. As the reported accuracy of stool DNA testing varies, Ahlquist and colleagues compared the effectiveness of this screening method with FOBT.

The multicenter, prospective study included 3,764 healthy adults (aged 50–80 years) at average risk for colorectal cancer who underwent colonoscopy. Participants sent stool samples (including smeared Hemoccult® and HemoccultSensa® [both of Beckman Coulter, Fullerton, CA] FOBT cards) by express mail to the Mayo Clinic in Rochester, MN, for analysis. Colonoscopy detected relevant neoplasms in 290 patients. Stool DNA test 1, a precommercial 23-marker assay, was carried out in 2,497 patients and detected 20% of cancers and precancerous polyps, compared with 11% detection by Hemoccult® and 21% by HemoccultSensa®. Stool DNA test 2, which assesses three broadly informative markers, was used for a subgroup of 217 patients, and detected 46% of cancers and precancerous polyps, compared with 16% detection by Hemoccult® and 24% by HemoccultSensa®.

The researchers point out that the increased sensitivity of stool DNA test 2 was particularly noticeable for adenomas, although this test did produce more false-positive results than did other methods.