Early optimism for new DNA-based test for colorectal cancer

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A study conducted by the technology s developer but not yet published shows some cause for optimism in non-invasively diagnosing the 2nd leading cancer killer in the U.S., colorectal cancer (CRC). The test, made by Exact Sciences Corp. and called Cologuard , uses immuno-chemistry to seek DNA alterations mutations, in other words characteristic of CRC in a sample of feces, or stool. While the company did not release the specifics, the study involved 10,000 people with an average risk of CRC, evaluated at 90 different centers in North America.

The results were, if not groundbreaking, at least gratifying: the test correctly found 42 percent of precancerous polyps, and 92 percent of cancers. Viewed another way, the test missed 8 percent of cancers a not-insubstantial false-negative rate. The false-positive rate of 13 percent means that those patients underwent colonoscopy, the gold standard of CRC diagnosis (and often, treatment), and no polyps or tumors were found.

This is a potentially important addition to the other non-invasive tools for CRC detection: stool occult blood and immuno-chemical tests on stool for occult blood, rather than this new test for aberrant DNA, and colon CT scan with contrast. Other invasive tests are also done, including sigmoidoscooy (often accompanied by an XRay test, the barium enema), and colonoscopy.

CRC kills about 52,000 Americans each year out of 143,000 diagnosed with the disease. If everyone followed the guidelines of the academic societies, CRC might be nearly wiped out, as colonoscopy at age 50 and every few years thereafter (depending on personal history and clinical findings) would find a large majority of both cancers and pre-malignant polyps. The problem is, fewer than 1/2 of those who should be studied go through with the test, because it is invasive, time-consuming, expensive and some find it embarrassing. Unfortunately, none of the other tests allow a person to avoid colonoscopy with assurance, as they all miss a certain percentage of cancers and pre-cancers.

ACSH s Dr. Gilbert Ross says the message is clear: while this test may be fine-tuned over the next few years, anyone 50 or over, or with other risk factors including family history or bloody stool, should discuss colonoscopy and CRC with his or her doctor.