ST. PAUL, MINN — ST. PAUL, Minn. -- A common blood test used to detect a recurrence of colon cancer is highly unreliable and expensive and can lead to needless tests and even surgery on healthy patients, researchers at the Mayo Clinic and elsewhere say.
The procedure -- called a CEA test -- identifies a protein-like substance called carcinoembryonic antigen. The antigen may be produced in large quantities by cancer in the large bowel and can be accurately identified in blood.
But in a study published in today's Journal of the American Medical Association, researchers said that the test has such a low success rate that it should be abandoned.
"We found the test extremely unreliable and hope that it will be abandoned," said Dr. Charles Moertel, professor of oncology at the Mayo Clinic in Rochester, Minn., and chief author of the study.
Dr. Moertel said his research team hopes that the study stimulates a search for a better way to give colon cancer patients a second chance.
When the CEA test was developed about 20 years ago, some believed that it could be used as a screening tool for colon cancer, the nation's second-leading cancer killer after lung cancer.
Although follow-up research showed that the test was too insensitive to serve as a screen, it became the standard way to monitor patients after colon cancer surgery.
To determine the test's effectiveness, researchers at the Mayo Clinic, the Fred Hutchinson Cancer Research Center in Seattle, the Temple University School of Medicine and the University of Pennsylvania, both in Philadelphia, and the Grand Forks Clinic in Grand Forks, N.D., followed 1,216 patients who had undergone colon cancer surgery. Of those, 1,017 were being monitored by CEA testing.
"The fundamental objective of the test is to pick up a recurrence at a stage when it can be cured," Dr. Moertel said. But one-year survival rates for study participants who experienced a recurrence was 2.3 percent for those who underwent CEA monitoring and 2 percent for those who did not.
Dr. Moertel said there are two major problems with the test.
About 40 percent of patients have false negatives, which means that many colon cancers go undetected until they have spread.
About 20 percent of patients have false positives. To rule out a recurrence, they must unnecessarily endure numerous tests, such as coaxial tomography and magnetic resonance imaging scans, endoscopies and barium X-rays.