The researchers found that having a complete colonoscopy was strongly linked to a lower death rate related specifically to colon cancer on the left side of the organ. But, the screening process showed virtually no death-prevention benefit with right-sided colon cancer.
Both findings applied equally across gender and age.
In an accompanying editorial in the journal, Dr. David F. Ransohoff, a professor of cancer epidemiology at the University of North Carolina, suggested that the mortality risk reduction offered by colonoscopies is probably closer to 60 percent to 70 percent, rather than the 90 percent figure typically cited.
Baxter said there are probably several factors that contribute to the left side/right side discrepancy.
"For example, there are differences in how polyps grow," Baxter said. "They tend to be flatter on the right side, which is harder to pick up and harder to take out when you find them."
"But the overall quality of colonoscopies is improving," she added. "And, meanwhile, there are some things that patients can do to improve pick up on the right side, such as complying well with their preparations. Many do already, but many kind of give up after part of the preparation is done. So, there are a lot of people who don't get through 100 percent of the prep. And I think it's important that they do so."
Dr. Judith Collins, section chief of gastroenterology at the VA Medical Center in Portland, Ore., said that despite the apparent limitations highlighted in the new study, colonoscopies are still the gold standard for detection of colorectal cancer.
"This is a totally preventable cancer," she said. "So whether screening for it results in a 60 percent reduction in death or 90 percent reduction, there's just no other cancer that we can see this well, and colonoscopy certainly reduces mortality. And that's the bottom line. There are a lot of variables that show t
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