By Anthony J. Brown, MD
NEW YORK (Reuters Health) – Analyzing fecal DNA for mutations of the adenomatous polyposis coli (APC) gene can identify early cases of colorectal cancer, according to a report published in the January 31st issue of The New England Journal of Medicine.
Dr. Bert Vogelstein, from The Johns Hopkins School of Medicine, Baltimore, and colleagues obtained stool samples from 28 patients with nonmetastatic colorectal cancers, 18 patients with adenomas that were at least 1 cm in diameter, and from 28 control patients without neoplastic disease. DNA was extracted from the samples and screened for APC mutations, using a novel approach known as digital protein truncation.
The researchers found that 26 of the 46 patients with neoplastic disease and 17 of the 28 cancer patients had APC mutations. In contrast, no mutations were identified in any of the patients without neoplastic disease. In patients with positive tests, the mutant genes accounted for 0.4% to 14.1% of all APC genes found in the stool.
"We envision this test being used for patients at average risk for colorectal cancer," Dr. Vogelstein told Reuters Health. "We expect it to supplement other screening tests, not replace them," he said. "The idea is to offer physicians greater flexibility in choosing a test and thereby enhance screening participation rates."
Dr. Vogelstein believes that "in an average risk patient the sensitivity of the test could easily reach 70%." The specificity "is going to be close to 100% because the test is clearly based on the pathogenesis of colorectal cancer," he added. "These figures compare favorably with those of other screening tests such as Pap smear and mammography, which have saved a lot of lives."
The test is "noninvasive and, unlike occult blood screening, it doesn't require three sequential stool specimens," Dr. Vogelstein pointed out. "Hopefully, having such a well tolerated test will increase the number of people who get screened."
In a related commentary, NEJM editor Dr. Robert S. Schwartz notes that while the APC stool test "is clearly not ready for clinical application," it is "a step in the arduous journey toward a reliable, noninvasive molecular screening test for colorectal cancer."
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