When detected and treated early, colorectal cancer is a curable disease. In fact, the cure rate is better than 90 percent when it's discovered at its earliest stage. However, only about half of Americans get the screening that they deserve, and far too few colorectal cancers are discovered early enough. And the bad news is that once the cancer has spread to nearby organs or lymph nodes, the five-year relative survival rate is 65 percent.
There are several recommended strategies for catching colorectal cancer at its earliest stage. Colonoscopy is probably the most effective screening test. A new imaging technology, called virtual colonoscopy, may offer a more appealing alternative.
With conventional colonoscopy, a camera at the end of a long flexible tube (called a colonoscope) is inserted through the rectum and into the colon. The doctor can then examine the lining of your colon on a video monitor. To undergo this invasive test, you are sedated. With sedation, you are required to have someone drive you to and from the test.
In comparison, virtual colonoscopy usually takes less time, and no sedation is necessary. A detailed and thorough computed tomography (CT) scan is taken of your pelvis and abdomen in less than a minute. Computer software then transforms this scan into a three-dimensional view of the inside of your colon. Your doctor can view your colon almost as clearly as with conventional colonoscopy. Currently, you still need to take a laxative the night before the CT scan in order to clean your bowel. And a small rectal tube is inserted during the test so that air can be put into the colon to improve the CT scan images.
In clinical trials, virtual colonoscopy has begun to demonstrate its worth in comparison with conventional colonoscopy. What it does best is detect moderate-sized polyps or abnormalities larger than six millimeters. It also has a reasonably low rate of false alarms. (A "false-positive" finding turns out to be normal with further testing but leads to unnecessary medical procedures, as well as anxiety.) What it doesn't do as well as conventional colonoscopy is detect polyps that are small.
Polyps present another problem for virtual colonoscopy — how to remove them. When polyps are discovered during a conventional colonoscopy, they can be removed at that time. But what if polyps are discovered during a virtual colonoscopy? You'll have to undergo a conventional colonoscopy, after all, to have them removed.
Before virtual colonoscopy can be offered to everyone as a screening test, experts believe more research needs to be done. This means finding out if people tested with virtual colonoscopy are less likely to develop colon cancer and live longer and healthier lives. Also, because virtual colonoscopy does not have proven value compared to conventional screening methods, most insurers will not cover the costs.
For now, experts believe virtual colonoscopy best serves people with medical conditions, such as bleeding disorders, severe lung disease, or critical heart problems, that exclude them from conventional colonoscopy. It's also a good alternative for people who cannot tolerate the sedation necessary with conventional colonoscopy.
And what about those of us who are just squeamish? Well, if you're at a high risk of colorectal cancer, then most doctors agree, a virtual colonoscopy is certainly better than no screening at all. And in the future, who knows? Perhaps virtual colonoscopy will someday play an important role in bringing more of us in for colorectal screening.
Another new, simple noninvasive screening test for colorectal cancer involves DNA testing. Precancerous polyps and tumors from early-stage colon cancer shed cells into the intestine. Many of these cells contain abnormal DNA indicating cancerous changes.
DNA testing can detect these abnormal cells in stool samples. In clinical trials thus far, DNA testing has proven more accurate in detecting colorectal cancer than the fecal occult blood test, another screening method that uses stool samples. Experts believe if clinical trials continue to produce favorable results then this test could become a standard screening procedure within a few years.