New test may detect colon cancer in earlier stages.
Colon tumors shed blood and cells that are detected in stools, but tests for blood have reduced deaths from colon cancer only modestly because they are not very sensitive to precancerous polyps, when the cancer is most easily treated. The new test being developed detects methylation of tumor suppressor DNA at four markers, which allows it to distinguish colon tumors and polyps from normal tissue with great sensitivity and no false positives.
Although the test on stools is expected to be less accurate than tests performed directly on tumors, the researchers expect that it will detect at least half of all precancerous polyps and 85% of actual cancers.
The trial to validate the test is now under way on 1,600 patients, and results will be reported in October. If validated, the test is expected to cost $300 and can be done at home. Patients would be advised to take the test once every three years. People with a positive test would be referred for a colonoscopy to verify and remove polyps. If the test works as hoped, it will be the first noninvasive test to reliably detect malignant tumors and should be able to reduce colon cancers similarly to the way the Pap test reduced cervical cancers.
According to the researchers, other types of cancers of the gastrointestinal tract, such as pancreas, esophagus, and stomach, which account for a quarter of all cancer deaths in the United States, could be detected from stool samples using different sets of four markers. However, with colon cancer, the stool test's 90% sensitivity and 5%-10% false-positive rate is tolerable because it can be confirmed by colonoscopy. With other cancers, the false positives would be more of a problem because there is no easy verification method like a colonoscopy.
Ericson, K., Gan, C., Cheong, I., Rago, C., Samuels, Y., Belculescu, V.E., ... Papadopoulos, N. (2010). Genetic inactivation of AKT1, AKT2, and PDPK1 in human colorectal cancer cells clarifies their roles in tumor growth regulation. Proceedings of the National Academy of Science of the United States of America, 107, 2598-2603.
[By Deborah McBride, RN, MSN, CPON[R], Contributing Editor]
Contributing Editor Deborah McBride, RN, MSN, CPON[R], is a staff nurse III at the Kaiser Permanente Oakland Medical Center and an assistant professor at Samuel Merritt University in Oakland, CA.
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|Date:||Oct 1, 2010|
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