Jan. 3, 2011 -- It is considered one of the most effective cancer screening and prevention exams, but recent studies have raised concerns that a colonoscopy may not be useful for detecting certain colorectal cancers.
Now a new study from Germany offers strong evidence that the test can prevent colorectal cancers located throughout the colon -- not just those easiest to reach with the fiberoptic imaging scope.
Experts say the findings should reassure patients that a colonoscopy saves lives by detecting and removing precancerous polyps throughout the colon before they can become malignant.
The study appears in the Jan. 4 issue of Annals of Internal Medicine.
“This study tells us that when done well, colonoscopy is effective in both the left and right side of the colon,” Fox Chase Cancer Center director of gastroenterology David S. Weinberg, MD, tells WebMD.
Right-Side Polyps May Be Harder to Spot
Worldwide, more than a million people are diagnosed with colorectal cancer each year, and about half a million people die of the disease.
Colonoscopy involves a flexible fiberoptic scope with a video camera, which is threaded through the large intestine to search for and remove polyps before they become malignant. Widely performed in the U.S. and Europe, it is considered the most effective screening tool for colorectal cancer.
It is used to visualize the entire large intestine, including the section farthest away from the rectum.
But several recent studies from Canada have raised doubts about the effectiveness of colonoscopy in this area, known as the right side of the colon.
In one study, researchers in Ontario failed to find evidence that colonoscopy screening reduced deaths from right-sided colorectal cancers, although a survival benefit was seen in patients with left-sided cancers.
In another study, researchers from the University of Manitoba found that colorectal cancers occurring on the right side of the colon appeared to be missed during colonoscopy far more often than cancers occurring on the left side.
Reduction in Right-Side Cancers
In the newly published study, investigators from the German Cancer Research Center compared the colonoscopy histories of close to 1,700 colorectal patients living in southwest Germany with 1,900 people without cancer matched for age, sex, and place of residence.
Study participants were asked whether they had had a colonoscopy during the previous 10 years, and patient medical records were analyzed.
After taking into account known colorectal cancer risk factors, colonoscopy screening within the previous decade was associated with a 77% overall reduction in colorectal cancer risk.
The risk reduction was 84% and 56%, respectively, for left-sided and right-sided cancers. In patients younger than age 60, however, screening was associated with a 26% reduction in risk in right-sided cancer, which was not statistically significant.
The reduction in risk was seen for all cancer stages and for both men and women.
In an editorial published with the study, Weinberg writes that while it is not entirely clear why colonoscopy is not as effective in the right colon, it would be a mistake to conclude that it is ineffective.
He tells WebMD that the newest findings do not necessarily contradict those of the Canadian studies because those studies also showed protection against right-sided cancers when colonoscopies were performed by doctors who had a high polyp detection rate.
Douglas K. Rex, MD, agrees, noting that the Canadian findings may reflect the fact that a large proportion of colonoscopies in that country are performed by surgeons and primary care doctors and not gastroenterologists who specialize in the exam.
A gastroenterologist himself, Rex is a distinguished professor of medicine at Indiana University School of Medicine and he is the co-author of the American College of Gastroenterology’s screening guidelines for colorectal cancer.
“This is a procedure that requires a certain amount of skill,” he says. “But that doesn’t mean that every gastroenterologist does this exam well.”
Two Key Questions Every Patient Should Ask
In the U.S., screening for colorectal cancer is recommended to start at age 50 for people at average risk and at a younger age for those who have an increased or high risk for the cancer.
But Rex says doctors who perform colonoscopies in the U.S. are not required to document the thoroughness of the exam.
This is not the case in Germany, where quality assurance measures have been introduced nationwide.
While it is not as easy for patients in the U.S. to know if they are getting a high-quality colonoscopy, Rex says every patient should ask two key questions when they schedule their exam:
- What is the polyp detection rate of the practitioner performing my colonoscopy?
- Can I see documentation that my colonoscopy will cover my entire colon?
Polyps occur in about 25% of men and 15% of women aged 50 and over who have the exam. A rate much lower than this may indicate a less than thorough examiner, Rex tells WebMD.
Likewise, asking for evidence that the colonoscopy covered the entire colon, which may include a photograph of the point of the large intestine furthest from the rectum, known as the cecum, could lead to a more thorough exam.
“Patients can help make colonoscopy better by demanding evidence that the doctor performing the exam has followed these quality measures,” he says.