DNA testing may help detect colon cancers earlier

(CNN) -- Preliminary study findings show that a new genetically based screening test may spot colon cancers and polyps early enough to make a real impact on survivability.

The test measures DNA markers that are specific to cancerous and pre-cancerous cells. The Mayo Clinic in Rochester, Minnesota, found the test was able to detect 91 percent of cancers and 73 percent of pre-cancerous polyps in a study being published in the November issue of the American Journal of Gastroenterology.

"This is exciting," said Sudhir Srivastava, chief of the cancer biomarkers research group at the National Cancer Institute in Washington. "This could replace the fecal occult blood test."

Mayo researchers, working with a Massachusetts company, EXACT Laboratories Inc., are now undertaking a larger study involving several thousand patients, which is expected to take up to three years.

Replacing the fecal occult blood test -- a standard screening tool for years -- is premature, but preliminary results are very promising, said Dr. David Ahlquist, a lead study researcher who directs the colorectal neoplasia clinic at Minnesota's Mayo Clinic.

"This approach is dramatically different in that it measures not blood, but it measures DNA in the stool -- DNA that is shed from the lining of polyps and cancer, kind of like leaves falling off the trees in autumn," continued Ahlquist, explaining that such DNA changes are "like a fingerprint."

Testing for hidden blood in the stool can be inaccurate, and may miss some tumors or polyps that do not bleed. Still, said Ahlquist, "its benefit is that it detects (cancers) at a slightly earlier stage, therefore a slightly more curable stage."

Other tests such as sigmoidoscopy and colonoscopy involve inserting telescopic instruments into the rectum. Doctors believe fear of these tests is one reason many people do not participate in screenings. Preparatory purging of the intestinal tract, as well as sedation during the test itself, can be unpleasant. In addition, there is the risk of colon perforation, which could require surgical repair.

As it is, some 70 to 80 percent of people in the United States don't get regular colon cancer screening, according to Dr. Laura Seeff, an epidemiologist at the Centers for Disease Control and Prevention in Atlanta, Georgia.

The Mayo Clinic study followed 61 patients -- 33 with previously diagnosed colon cancer or pre-cancerous polyps, and 28 with normal colons. There were no false-positive readings in those who had normal colons, researchers said.

Studies using different genetic markers at Johns Hopkins University Medical Center in Baltimore, Maryland, have yielded similar results. The National Cancer Institute is funding studies on the Hopkins test, as well as others at the University of Michigan and Mayo.

"This new, non-invasive test safely and accurately detected curable-stage cancer of the colon and rectum," said Ahlquist.

Colorectal cancer is the second-leading cause of cancer death in the United States, affecting some 130,000 people a year. About 56,000 die each year from colon cancer.

CNN Medical Correspondent Elizabeth Cohen contributed to this report.

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American Cancer Society
Centers for Disease Control and Prevention: Colorectal cancer information
Colorectal Cancer Network
Mayo Clinic
EXACT Laboratories Inc.
National Cancer Institute
American Journal of Gastroenterology

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