July 19, 2000 -- Colorectal cancer is a killer. It attacks silently, usually making its presence known only when it cannot be stopped. But colorectal cancer doesn't start out deadly. It develops from growths in the rectum and colon called polyps, which aren't yet cancerous. If detected early, the growths are removed and cancer will most likely be prevented.
Many leading experts say the best way to find and remove those growths is to examine the whole length of the colon using a tiny scope that allows the doctor to carefully view the inside walls. Called colonoscopy, this procedure recently gained additional prominence when TV personality Katie Couric underwent one on TV. Now two studies in the July 18 issue of The New England Journal of Medicine offer more proof that colonoscopy may be the most effective way to screen for colon cancer.
Some background: The best technique for screening the colon is a controversial subject. Some doctors advocate the use of flexible sigmoidoscopy, a procedure that looks at just the lower part of the colon and can be performed in the doctor's office. Colonoscopy, on the other hand, can look for cancers throughout the whole colon but requires anesthesia. To further confuse the issue, many doctors recommend yearly testing of the stool for blood, sometimes an early sign of cancer. This test is also very controversial.
In one study, a group of researchers used colonoscopy to screen more than 3,000 healthy male volunteers aged 55 to 75. They found early cancers in almost 10% of those screened. David A. Lieberman, MD, lead author of the study, tells WebMD that these men had no symptoms, and adds that colonoscopy is probably the only tool that could have located the cancers due to their location. Lieberman is a professor of medicine and chief of the division of gastroenterology at the Oregon Health Sciences University in Portland.
Lieberman concludes that colorectal cancer screening using colonoscopy is the way to go "because most lesions begin as precancerous growths that we can detect and remove and thus prevent cancer." That possibility makes a compelling case for use of the most effective screening tool, he says.
The second study in the journal attempted to determine whether the presence of polyps in the lower area of the colon is a marker for cancers higher in the colon. The researchers thought that if a lower polyp predicts the presence of a cancer higher up, then flexible sigmoidoscopy may be an adequate screening tool. The scientists analyzed almost 2,000 patients with no symptoms over the age of 50 who underwent initial colonoscopy. Twelve cancers -- eight in men -- were detected by the screening.
The scientists found that the presence of a polyp in the lower colon does increase the likelihood that the person has a colon cancer farther up. However, one of the study's authors, Thomas F. Imperiale, MD, tells WebMD that more than half of the people with cancer high in the colon -- beyond the range of the flexible sigmoidoscope -- had no polyps close to the rectum.
Because colonoscopy is expensive -- about $1,000 -- and requires that patients be given anesthesia, some experts have suggested that it should be reserved for those patients who have polyps detected using the far less expensive flexible sigmoidoscope. But Imperiale says that strategy would miss nearly half of the polyps that could lead to cancer, as he found in his study. Having said that, Imperiale, who is an assistant professor of medicine at Indiana University School of Medicine in Indianapolis, says he doesn't favor colonoscopy for everyone.
"My take is that there should be a more balanced approach. I do think we need to be more liberal in the use of colonoscopy, but our long-term goals should be to find ways to estimate risk more accurately," Imperiale says. He says that abandoning flexible sigmoidoscopy in favor of colonoscopy is "going to the other extreme ... remember, the vast majority of patients in our study and other studies had no polyps." Imperiale says he differs from many of his colleagues in that he takes a conservative approach to colonoscopy. "We don't have high enough numbers to say with great confidence who does and who doesn't need colonoscopy," he says.
Douglas Rex, MD, is one of the authors of the American College of Gastroenterology's current screening guidelines. Those guidelines recommend a first colonoscopy at age 50 for those with average risk and a follow-up colonoscopy every 10 years thereafter. Rex tells WebMD that "Imperiale tends to be very cautious. There is a significant jump in colon cancer beginning at age 50 and continuing through age 60, and then it levels off with age." Rex is a professor of medicine at Indiana University and is a partner in the same practice as Imperiale.
David A. Johnson, MD, also a co-author of the guidelines, says he too thinks both studies make the case for colonoscopy.
Johnson, a professor of medicine at Eastern Virginia Medical School in Norfolk, says, "Colonoscopy is the best evolving screening modality that we have, and it should be utilized without waiting for symptoms." He says that for some reason -- possibly a change in diet or other environmental factor -- colon cancers have moved from their historic location low in the rectum to higher in the colon.
He adds that screening tools have also evolved from the rigid sigmoidoscope, which was adequate in the 1930s, to the use of flexible sigmoidoscopy. "But with this tremendous shift in position, even with the flex sig you can't get in there. That's why in the last several years, there has been a recognition of the need for whole colon imaging."
Johnson says the American College of Gastroenterology is so pro-colonoscopy that it has decided to launch an effort in "10 to 15 key states, including New York, to introduce model legislation that will require health insurance companies to cover screening colonoscopy." He says that Virginia already has such a bill, which was introduced by state Sen. Emily Couric, sister of TV personality Katie Couric, whose husband died as a result of colon cancer. He says the state campaigns will begin in full force this fall.
- Colorectal cancer doesn't usually cause any symptoms in the early stages of the disease, when it is most treatable, so it is important to be screened to discover any growths that could lead to cancer.
- New research shows that colonoscopy is a superior screening method to flexible sigmoidoscopy, because it examines the whole length of the colon, not just the lower half.
- The use of colonoscopy is still somewhat controversial, because it is more expensive and requires anesthesia.