More Tolerable Colon Cancer Test May Encourage Screening
Sept. 24, 1999 (Minneapolis) -- A new way of screening for colon cancer may motivate more people to be tested, even though it's not as effective as conventional methods, according to an article in this week's issue of The Lancet. Computed tomography colonography, or virtual colonoscopy, takes less time and is less invasive than any of the tests that are usually performed, the authors write.
Although colon cancer is the second largest cause of cancer-related death, the authors note that only 40% of Americans who are at risk for it get screened. 'Virtual colonoscopy' may increase that number. That's because people typically find the screening methods for colon cancer distasteful, the authors write. For example, testing the stool for blood calls for patients to collect stool samples at home that are then sent to the doctor's office for testing. Barium enemas are also used, as is a procedure called a colonoscopy. That entails probe-guided imaging of the colon which can last 30 minutes or more.
The virtual colonoscopy takes approximately 10 minutes, the authors write. When undergoing the procedure, the patient's bowel is cleaned by the use of an enema the night before, as would be the case for either a barium enema or a colonoscopy. But the next day, a tube is inserted in the patient's rectum and the colon is inflated with air. The "patient is [then] moved through a continuously rotating X-ray beam of a ... [CAT] scanner during a single breath-hold," the authors write. The operator then obtains images of the patient's colon.
"This technique is expanding beyond the research realm, and [is being used] in several centers," co-author Jonathan B. Kruskal, MD, PhD, tells WebMD. He says that the virtual colonoscopy has particular advantages in patients who have had an unsuccessful colonoscopy, in which the probe cannot make its way through the entire colon.
"It's a little early to say that [virtual colonoscopy] will revolutionize [colon cancer] screening, but early indications are that it's a promising test," Bernard Levin, MD, tells WebMD in an independent interview. "It's very important to find out whether it can be done in many places, or whether it must be done in specialized centers. We also haven't seen whether it's applicable community-wide. More studies are needed, but it's promising." Levin is vice president of cancer prevention and professor of medicine at University of Texas M.D. Anderson Cancer Center in Houston.
Virtual colonoscopy is still being evaluated for its sensitivity in detecting growths, or polyps, says Kruskal, assistant professor of radiology at Harvard Medical School in Boston. "It's equal in sensitivity to barium enema for polyps one centimeter or larger," he tells WebMD. "Although it's less sensitive for smaller polyps, they're less likely to become malignant," says Kruskal, who is also a radiologist in the abdominal imaging section of Boston's Beth Israel Deaconess Medical Center.
Although virtual colonoscopy is expensive, its acceptance by patients may make it as cost-effective as other techniques. The procedure "typically takes no more than 10 minutes, does not require sedation or abdominal compression, and is well tolerated apart from mild discomfort due to air [inflation]," the authors write. "Patients who have undergone both procedures prefer [virtual colonoscopy] to either barium enema or colonoscopy."
However, virtual colonoscopy's advantage of minimal invasiveness does not hold for all patients; 25% may have to also undergo subsequent colonoscopy and therefore have a repeat enema. For those patients, unless the colonoscopy could be offered on a same-day basis, "the initial advantages of undergoing a minimally invasive [virtual colonoscopy would be] less appealing," the authors write.