MONDAY, Feb. 18 (HealthDayNews) -- For people who have already had surgery for colon cancer, a colonoscopy alone doesn't seem to provide the same protection it does for the general population.
That's what a study that appears in today's issue of the Annals of Internal Medicine has found.
Although a colonoscopy -- a procedure that can diagnose and remove pre-cancerous lesions -- has spared many the trauma of colon cancer, it may not protect as well against a second bout of the disease, say researchers from the University of Pennsylvania Cancer Center in Philadelphia.
"The take-home message is that physicians need to be aware that there is a significant rate of second [colon] cancers in people who have had them, and
despite our best efforts, to date, there is still a significant risk," says lead author Dr. Robert J. Green, now an oncologist at Good Samaritan Medical Center in West Palm Beach, Fla.
Green added one note of caution about the findings.
"It's important to realize that this study is not saying that colonoscopy doesn't work, because in the general population it is the best and most effective tool we have for preventing colon cancer," Green says.
Colonoscopy involves looking into the colon via a tube inserted through the rectum. It searches for abnormalities linked to colon cancer, including not only tumors, but also polyps. These small lesions may not be malignant, but they can sometimes be the precursor of colon cancer. Spotting and removing polyps early has been shown to prevent colon cancer from ever occurring.
However, doctors have now found that, for those who have already had surgery for colon cancer, a colonoscopy -- usually performed six months to a year later, and again in three to five years -- is not so effective at detecting risky conditions before a second colon tumor develops.
One reason, says the study, may be that the colonoscopies performed in this study were compared to those performed during a clinical trial, which simply may have produced more effective results.
"It's very difficult to duplicate what you get in a controlled environment in the general community," Green says.
Equally as important, however, the study points out the biology of cancer may be different the second time around.
For Dr. Mark Pochapin, a gasteroenterologist who believes the study is both valid and important, this is perhaps the most significant theory.
"Once someone has a colon cancer, I don't consider them average risk anymore," Pochapin says.
While it may take 10 or 15 years for a polyp to turn into a primary first cancer, Pochapin believes the process may be greatly accelerated in those who have already had the disease.
Even more importantly, both Pochapin and Green agree it's possible these "second primary tumors," or even pre-malignant polyps, are present when the first tumor is diagnosed, but go undetected.
"If, in the process of giving a colonoscopy, you discover a tumor and it's large, it can block you from seeing the rest of the colon. So, in essence, you don't really know if there are other tumors or other polyps beyond that site," Pochapin explains.
Likewise, Green says, once the tumor is removed, it can be difficult for surgeons to see beyond where the tumor was located.
Although not shown in this study, both doctors say the answer for cancer patients may be to make certain the entire colon is examined, either before surgery, if possible, or within a month of surgery, via colonoscopy.
"This is one way to rule out whether or not there are other tumors, or even some nasty-looking polyps, lurking in the colon," Pochapin says.
The study, which began in 1989, involved 3,278 colon cancer patients treated with both surgery and chemotherapy. Their cancer had not spread beyond the intestines or to the nearby lymph nodes.
The doctors collected data on the patients every three months for the first year, every six months for the following four years, and every year after that until death or the end of the study. This included any surveillance procedures that were done, when they were done, and whether or not a second primary colon cancer was detected.
They compared their findings against the general U.S. population during this same time period, as well as with patients who participated in the National Polyp Study -- a research project that measured the effectiveness of colonoscopy in reducing colon cancer.
Despite regular colonoscopies, the rate of second primary colon cancer remained much higher in the group that had colon cancer than in either of the two comparison groups.
In addition, the new cancers cropped up relatively soon after routine colonoscopies.
What the study shows, Green says, is that better prevention strategies are needed to reduce the rate of colon cancer's return.
What To Do
For more information on colon cancer, visit The American Society of Colon and Rectal Surgeons or the American College of Gastroenterology.
To learn more about how a colonoscopy is performed and how it can save your life, check out The National Institute of Diabetes and Digestive and Kidney Diseases. To learn about the newest 3D Virtual colonoscopy, go here.
