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Posted on Dec 27, 2004, 1 p.m.
By Bill Freeman
A test that looks for cancer DNA in stool seems to be better at finding colon cancer than the traditional test for blood in the stool. But neither test performs as well as colonoscopy, researchers report in the New England Journal of Medicine (news - web sites) (Vol. 351, No. 26: 2704-2714). The DNA test is a relatively new test that doctors hope could one day become another option for finding colon cancer early.
A test that looks for cancer DNA in stool seems to be better at finding colon cancer than the traditional test for blood in the stool. But neither test performs as well as colonoscopy, researchers report in the New England Journal of Medicine (news - web sites) (Vol. 351, No. 26: 2704-2714).
The DNA test is a relatively new test that doctors hope could one day become another option for finding colon cancer early. Because it is easy and non-invasive, people might prefer it over tests like colonoscopy or sigmoidoscopy, said lead author Thomas Imperiale, MD, a professor of medicine at Indiana University School of Medicine.
But first, doctors must show that it works as well as -- or better than -- other accepted colon cancer tests.
To do that, Imperiale and colleagues from the Colon Cancer Study Group gave 3 screening tests to more than 2,500 people. All were age 50 or older (the age at which the American Cancer Society (news - web sites) recommends beginning screening), with no symptoms of colon cancer and an average risk of developing the disease.
The study participants first gave a stool sample to be used for the DNA test. Then they each completed a fecal occult blood test (FOBT). For this test, people must smear a small amount of stool onto a card, then submit it to the doctor for examination. Getting an FOBT every year is one of the colon cancer screening options the American Cancer Society (ACS) recommends.
Finally, the participants had a colonoscopy -- a visual exam of the colon using a tiny camera on the end of a flexible tube. This test is considered the "gold standard" of colon cancer screening because it can find nearly every cancer or precancerous growth (polyp) and remove growths before they become cancerous. Getting a colonoscopy every 10 years is another ACS screening option.
Don't Give Up the FOBT Yet
When the researchers compared their results, the DNA test found 52% of the colon cancers that colonoscopy found, while the FOBT found just 13%. The DNA test found 18% of dangerous polyps, and the FOBT found 11%.
But the results don't mean it's time to scrap the FOBT in favor of the DNA test, experts said.
It’s not yet clear there’s enough evidence that the DNA test works better, noted Robert Smith, PhD, director of cancer screening for ACS.
The performance of the FOBT in Imperiale's study was "unusually poor," Smith said. In other studies, the FOBT has been able to detect many more cancers than it did in Imperiale's. Other studies also have shown that an FOBT can reduce the incidence of colon cancer and the risk of death from the disease.
Cost is another issue, said Steven H. Woolf, MD, MPH, who wrote an editorial in the same issue of the journal. An FOBT costs between $3 and $40, while the DNA test costs $400-$800. It's also not clear that people would be any more willing to collect an entire stool sample for DNA testing than they are to take smears for an FOBT, he said.
The DNA test does have one big advantage, though: As more is learned about colon tumors and how they develop, it may be possible to make the DNA tests even more accurate than they are now.
Findings about fecal DNA testing will be among all the evidence ACS considers when it is time to revise guidelines for colon cancer screening, Smith said.
