A study presented today by Mayo Clinic researchers at the American Association for Cancer Research (AACR) Annual Meeting 2012 in Chicago identified two genes that are optimal targets to be analyzed in a new noninvasive test for colorectal cancer developed by Mayo Clinic, in collaboration with Exact Sciences Corporation. The test uses a small sample of a patient's stool to check for specific DNA changes, known as gene methylation, that occur as cancer develops. The test can quickly detect both early stage cancer and precancerous polyps.
"This study provided a means to refine our stool test and to minimize false-positive results, which can lead to unnecessary expense and cause patients undue stress," says principal investigator David Ahlquist, M.D., of Mayo Clinic.
The study involved 500 patients, ages 50 to 80, who had no symptoms and who recently had a colonoscopy with normal results. Researchers examined genes from each patient and found methylation increased among older patients. However, two genes were affected only minimally by age, making them optimal targets for the stool test. Importantly, the methylated genes were not affected by any other patient characteristics, including race, ethnicity, gender, geographic residence, family history of colon cancer, or previous polyps.
In addition, results of the stool test were consistent, regardless of whether patients smoked, consumed alcohol, took aspirin or were obese.
"Other than age, common clinical factors had no impact on the degree of methylation detected by the stool test," Dr. Ahlquist says. "This is very good news from the point of view of clinical practicality because the test applies to all patients, and they don't need to change medications or any habits for the results to be accurate."
A lab that reviews the test results can easily adjust the range of "normal" for older patients who undergo the test.
Previous studies by Mayo Clinic and Exact Sciences Corporation have shown that the stool test has high sensitivity for cancer and precancerous polyps.
"Because the test detects polyps, widespread screening with this test has potential to prevent colorectal cancer from forming in the first place, just as the Pap smear has prevented cervical cancer," Dr. Ahlquist says.
The stool test is being evaluated in a large multicenter study in the United States and Canada, involving 10,000 patients at more than 60 medical centers. If the test is approved by the Food and Drug Administration, it could become available to patients as early as mid-2013.
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