During screening exams, doctors look for small cancers and for growths called polyps, which may be precursors of cancer. Colon cancer is highly treatable if discovered early.

Colon cancer screening guidelines established by the American Cancer Society (ACS) are not followed as they should be because current screening procedures such as colonoscopy, flexible sigmoidoscopy, and barium enemas are costly and poorly accepted by patients, said Bernard Levin, MD, vice president of cancer prevention at M.D. Anderson Cancer Center in Houston and chairman of the ACS's colorectal cancer advisory group.

In colonoscopy and flexible sigmoidoscopy, a slender, flexible, lighted tube is placed through the anus and advanced into the colon. This allows the doctor to look at the inside of the large bowel for cancerous growths or for polyps. For a barium enema, the patient is given barium sulfate, a chalky substance used to coat the lining of the large bowel so polyps and cancers can be seen on x-ray films. Before having the tests, the patients must take laxatives and sometimes enemas. These tests are somewhat uncomfortable but not painful.

The new technique may be more acceptable to patients because it uses magnetic resonance imaging (MRI) and a process called fecal tagging that does not require bowel cleansing or involve radiation. "Instead of cleansing the colon, the patient merely has to add a small amount of neutral-tasting contrast material to the meals preceding the exam," said Jörg F. Debatin, MD, chairman of the department of radiology at University Hospital in Essen, Germany. "The stool is thus tagged and can remain inside the colon for the exam." Dr. Debatin and his colleagues published a brief article about their findings in a recent issue of the British journal The Lancet (Vol. 354, No. 9,181).

While fecal tagging has been studied by various scientists, Dr. Debatin and his colleagues have focused on ways to use the process with MRI rather than other imaging devices. Besides using magnetic fields instead of radiation, an advantage of MRI is it allows the doctor to get a three-dimensional view of the colon as well as look at areas outside the colon wall, such as the liver, during the same screening, Dr. Debatin said.

The process is noninvasive, the contrast agent added to the patient's food is safe, and the enema given before the screening does not hurt, Dr. Debatin said. If clinical trials prove that the technique is safe and effective, the only drawback to widespread acceptance might be the cost of the contrast agent, he added. The search for alternative agents will be part of ongoing studies of fecal tagging.

While the findings published in The Lancet were based on research with only two volunteers, at least 10 additional volunteers have now tried the fecal tagging procedure, Dr. Debatin said. In all cases, the volunteers had no significant side effects, and doctors were able to get an unobstructed view through the colon. Clinical trials in Europe are being planned, but it will be at least two years before the technique is widely available.

"Potentially, it's a very powerful concept," said Dr. Levin. If current ACS screening guidelines were followed, the incidence of colon cancer could be reduced by 50 percent, and noninvasive techniques such as fecal tagging with MRI could encourage more patients to undergo screening, he explained.

The ACS estimates 94,700 cases of colon cancer will be diagnosed in the US this year, and 47,900 people will die from the disease.