Colonoscopy Significantly Reduces Death From Left-sided Colon Cancer But Not From Right-sided
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A complete colonoscopy is a procedure where a physician inserts a long, flexible tube called a colonoscope up into the patient's rectum to scan the entire colon for potentially cancerous growths. If a polyp or lesion is detected, it can often be removed during the colonoscopy so that no additional procedures or surgery are needed.
Colonoscopy undoubtedly lowers deaths from colorectal cancer. However, the reduction appears to be entirely due to a reduction in deaths from left-sided cancers. A study published in the Annals of Internal Medicine concludes almost no reduction in deaths for cancer that develops in the right side of the colon. Colorectal cancer is the second-leading cause of cancer death in North America. The study appears today on the Annals of Internal Medicine Web site and will be printed in the January 6, 2009, issue: Association of Colonoscopy and Death From Colorectal Cancer: A Population-Based, Case–Control Study, Nancy N. Baxter, MD, PhD; Meredith A. Goldwasser, ScD; Lawrence F. Paszat, MD, MS; Refik Saskin, MSc; David R. Urbach, MD, MSc; and Linda Rabeneck, MD, MPH, 6 January 2009 | Volume 150 Issue 1:
"While colonoscopy remains the gold standard for evaluation of the colon, our study sheds light on some of the real-world limitations of this practice for screening and prevention," said Nancy Baxter, MD, PhD, Colorectal Surgeon and a Researcher at St. Michael's Hospital, who is lead author on the study.
Review of patient files was conducted for persons aged 52 to 90 who received a colorectal cancer diagnosis between 1996 and 2001 and died of colorectal cancer by 2003. These patients were compared to a control group who were selected from the population of Ontario and had not died of colorectal cancer. Colonoscopy was strongly associated with fewer deaths from left-sided colorectal cancer. But colonoscopy had no reduction of death for right-sided colorectal cancer.
"Colonoscopy is an effective intervention," said David F. Ransohoff, MD, author of an accompanying editorial. "The study results, however, should caution physicians about saying that colonoscopy will reduce the risk of dying from colorectal cancer by 90 percent. A 60 to 70 percent risk-reduction rate seems more reasonable."
As reported in Science Daily the difference can be explained:
The researchers suggest several reasons why colonoscopy may be less effective in preventing death from right-sided colorectal cancer. First, some colonoscopies considered "complete" may not evaluate the entire right colon. Second, bowel preparation may be worse in the right colon. Third, right and left colonic cancers and polyps may differ biologically. Right-sided growths may be less likely to have a fleshy stalk and are occasionally flat, which makes them harder to identify and remove, or they may grow more rapidly.
The researchers focus on tumor biology differences between right and left side tumors:
"Although improvements in the quality of screening colonoscopy may improve detection at the right side, differences in tumor biology may limit the potential to prevent right-sided colorectal cancer deaths with current endoscopic technology. Nevertheless, this study clearly demonstrates that colonoscopy is an effective procedure for the prevention of death from colorectal cancer, it just may not be quite as effective as we've thought in the past." said Dr. Baxter.
Both men and women should be regularly screened for colon cancer.