Widely used tests intended to detect signs of colon or rectal cancer miss more cancers than they catch, Mayo Clinic researchers say.
The researchers concluded Tuesday that the tests, which detect blood in a person's feces, are not good indicators of abnormal growths in the colon or rectum.The tests are used in highly publicized cancer-screening campaigns across the country and are endorsed by the American Cancer Society, the National Cancer Institute and others. Experts have recommended an annual stool blood test annually after age 50 in addition to physical examinations.
The Mayo Clinic researchers said one widely used test, using stool samples collected on pre-treated cards and mailed to a central laboratory for processing, missed more than 70 percent of colorectal cancers and more than 90 percent of intestinal polyps found in follow-up examinations.
A positive result on the "Hemoccult II" test truly predicted a cancer less than 10 percent of the time, the researchers said. The Hemoccult test is marketed by SmithKline Diagnostics of Sunnyvale, Calif.
The study, published in the Journal of the American Medical Association, involved more than 13,000 patients who took the tests.
The researchers also reviewed another screening test, HemoQuant by Mayo Medical Laboratories of Rochester, Minn., and SmithKline Beecham of Van Nuys, Calif. It was equally ineffective as a cancer screening tool, although it was more sensitive to fecal blood.
"The point is, it doesn't matter how well you detect blood in the stool," said Dr. David Ahlquist, a Mayo gastroenterologist who ran the study. "Fecal blood is a poor marker for colon cancer."