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Though not yet ready for common use, a new test may one day provide a more accurate, noninvasive way to detect colorectal cancers and adenomas (precancerous growths in the colon). Results from a pilot study of the new test were reported in the November 2000 issue of the journal Gastroenterology.

While colorectal cancer remains the third leading cause of cancer deaths in the United States, it can be cured if detected and treated early. However, many people avoid screening tests because the most definitive procedures (a colonoscopy or sigmoidoscopy) are invasive and relatively costly. Simply testing for blood in a patient's stool sample is another way to screen for signs of cancer, but the standard Hemoccult blood test is less precise. Blood in the stool can signal a variety of gastrointestinal problems, including stomach ulcers.

The new test was developed by the EXACT laboratories, Inc.of Maynard, Mass., and studied in collaboration with researchers at the Mayo Clinic in Rochester, Minn., with funding from the National Cancer Institute. The test is done on a patient's stool sample and looks for characteristic genetic changes in cells shed from the surface of colon cancers and precancerous adenomas. These genetic changes serve as signals of possible colorectal cancer, and so can lead to a more accurate diagnosis than the Hemoccult blood test.

In their pilot study of the test, the Mayo Clinic researchers -- led by David Ahlquist, M.D. -- looked for these genetic changes in DNA taken from stored stool specimens that had come from 61 patients whose colonoscopies had found either colorectal cancer, adenomas or normal-appearing colons. The test detected 91 percent of the colorectal cancers and 82 percent of the adenomas. By comparison, the Hemoccult test on the stool samples from patients with adenomas detected none of these precancerous growths. Hemoccult tests had not been done on the patients with colorectal cancer.

Larger clinical studies are needed to determine the efficacy of this test for colorectal cancer in everyday medical practice. Towards this goal, a study comparing the new DNA test with the Hemoccult test in patients undergoing colonoscopy is being planned.

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