DNA stool testing is more effective in detecting colon cancer than a widely used stool test

Dec 22 2004

A study in the current issue of the New England Journal of Medicine concludes that DNA stool testing is more effective in detecting colon cancer than a widely used stool test, but a Virginia Commonwealth University family medicine and public health physician argues in the same issue that its superiority is still in doubt.

The study on which the Dec. 23 editorial is based concluded that DNA testing on stool samples found more cases of colorectal cancer than the current screening method of fecal occult-blood testing, which measures blood in the stool.

“Should we begin using the stool DNA panel as a screening test for colorectal cancer, perhaps replacing fecal occult-blood testing?” wrote Steven H. Woolf, M.D., professor and director of research in VCU’s Department of Family Medicine. “The short answer is ’no.’”

Woolf, a member of the National Academy of Sciences’ Institute of Medicine, wrote that several issues must be considered before such a move is made. Woolf conceded that the new test probably detects more cancers than fecal occult-blood testing, but said that uncertainty exists about how many additional cases it will detect and whether the benefit outweighs the risks.

For example, the public, which tends to view DNA technology as very precise, may not realize how often stool DNA testing can be wrong, Woolf said. If 100 people over age 50 received an abnormal result on a stool DNA test, only two would turn out to have cancer. The other 98 would need additional testing, including colonoscopy, to prove that the result was a false-positive, and many would still live with the fear that they have cancer, even if that’s not the case.

Woolf also wrote that the cost of the new test might become an issue. The test currently costs between $400 and $800, compared with between $3 and $40 for fecal occult-blood testing. Measured in terms of how much must be spent on testing to save one life, stool DNA might cost $47,700, whereas colonoscopy, which is almost twice as accurate in detecting colorectal cancer, costs only half as much per life saved.

Accessibility and acceptance of the DNA test also could be hurdles to widespread adoption, Woolf wrote. Not all laboratories offer the test, and not all health plans cover it. In addition, he wrote, some patients might find distasteful the DNA-test requirement that an entire bowel movement be collected and refrigerated, as opposed to the two smears from three consecutive stool samples that must be collected for the fecal occult-blood test.

In the editorial, Woolf argued that more can be done to improve the outcomes of colorectal cancer by making the public’s access to screening more systematic and of higher quality. Barriers in access and delivery are keeping Americans from receiving the tests they need, whether the tests are new or old, he wrote.

“Improving screening rates is a less-breathtaking accomplishment than are technological advances in testing, and is less likely to make the evening news,” Woolf wrote. “But it may do greater good, especially for those minority populations at greatest risk for dying from colorectal cancer.”