A new study showed that virtual colonoscopy was able to detect 90% of precancerous polyps larger than 10 millimetres, giving the patients a less expensive alternative to standard colonoscopy, which had the same accuracy. These non-invasive tests are as effective as old-fashioned colonoscopies and ready to be widely used for cancer screening, said Dr. C. Daniel Johnson, lead author of the study published in the New England Journal of Medicine.

Colon cancer is the second leading cause of cancer deaths in the United States and the third most common type of cancer. More that 56,000 people lose the battle with cancer each year. The American Cancer Society estimates almost 150,000 new cases of colorectal cancer for 2008 in the U.S. Screening for polyps is recommended at age 50, but people avoid standard procedures because they are unpleasant. They involve inserting a long and flexible tube in a patient’s large intestine (rectum and colon). A small video camera is attached to the colonoscope so that your doctor can take pictures or video of the large colon. The test helps find ulcers, polyps, tumors and areas of inflammation or bleeding. In some cases during colonoscopy, if a polyp or abnormal tissue is found, your doctor may remove it at that time. During the procedure, a tissue sample (biopsy) of the polyp may be taken for lab analysis to determine whether subsequent surgical removal of the tissue is needed.

The report published in the New England Journal of Medicine, which was the largest of this kind, involved 2,600 men and women tested at 15 medical centers. All participants were over the age of 50 and had no known significant risk factors for colon cancer. All patients received both a virtual and a traditional colonoscopy. Researchers found that the virtual technique detected 90% of precancerous polyps 10 millimetres or larger. The virtual version of the test is done mainly outside the body and uses an X-ray computed tomography or CT scanner.

Virtual colonoscopy, also known as CT colonography or CTC, which costs $600 to $1,200 – the standard colonoscopy is much more expensive – is effective and is less invasive compared with traditional colonoscopy, the study authors said.

C. Daniel Johnson, MD, professor of radiology at the Mayo Clinic in Scottsdale, Ariz, who led the study, and colleagues also found that CT colonography could detect 78% of polyps as small as 6 millimeters in diameter. The procedure failed to detect about one in ten of the largest lesions. Previous studies showed that standard colonoscopies also failed to spot about 5 percent to 10 percent of the lesions.

Both techniques require preparations, which are the patients’ biggest complaint. For the procedures to be accurate, the colon must be well prepared. It must be clear of stool and fluids that obscure the view of the colon and rectal lining.

The National Cancer Institute and the American College of Radiology Imaging Network funded the research.

A second study published in the same journal involved nearly 2,500 people with an average risk of colon cancer. All participants had an initial colonoscopy and patients who had no signs of precancerous polyps on an initial test had an extremely low risk of developing colon cancer in the next five years. “We found no colon cancer after five years, and the risk of advanced precancerous polyps was very low,” said the study’s lead author, Dr. Thomas F. Imperiale, a professor of medicine at Indiana University School of Medicine and a research scientist at the Regenstrief Institute in Indianapolis.

Both studies move the field of colon cancer screening forward, wrote Robert Fletcher, professor emeritus at Harvard Medical School in Boston, in an editorial accompanying the studies.