Colonoscopies do not have blind spots – they reduce colon cancer risk not only on the left side of the colon, but also on the right side, researchers from the German Cancer Research Center in Heidelberg revealed in an article published in Annals of Internal Medicine. These latest findings contradict some prior studies which suggested there were right-side “blind spots” regarding colonoscopies.

A colonoscopy is a test that allows the doctor to have an inside look at the patient’s colon and rectum. The physician uses a flexible tube, called a colonoscope, with a camera at the end. As the camera moves through the rectum the doctor watches everything on a monitor (screen) – the colonoscope can reach right to the end of the colon. The colonoscopy helps the doctor identify any abnormality, take a biopsy, or even remove a polyps there and then.

Dr. Hermann Brenner said that their large study found a 77% lower overall risk of malignancy among those who underwent colonoscopies.

A colonoscopy can reach the left side of the colon more easily, and the researchers found an even lower risk of malignancy for that side. However, Brenner and team stressed that for those undergoing the procedure, the reduced risk was still considerable for both sides.

The authors explained that colonoscopy has been demonstrated to significantly lower the chances of developing cancer. However, its value in the community has never been compellingly clear – some observational studies had indicated that there were lower benefits than those found in the National Polyp Study. Other studies had suggested there was only a benefit in reduced risk for the left side of the colon and the rectum, while the risk to the other side was unclear.

This latest study involved 1,688 colorectal cancer patients and 1,932 controls (without cancer). They were all aged at least 50 years and were matched geographically, as well as for sex and age.

Their findings revealed:

  • 1,023 of those in the study had undergone at least one colonoscopy in the previous ten years.
  • 793 of them were control participants (without cancer) and 230 participants with cancer.
  • Even though the greatest risk reduction was for left-sided cancers, there was still a 50% reduction on the right side
  • Risk reduction was similar for males and females, regardless of cancer stage

The authors concluded:

“Colonoscopy with polypectomy can be associated with strongly reduced risk for CRC in the population setting. Aside from strong risk reduction with respect to left-sided CRC, risk reduction of more than 50% was also seen for right-sided colon cancer.”

In an Accompanying Editorial, Dr. David Weinberg, of the Fox Chase Cancer Center, Philadelphia, wrote that the study helped vindicated colonoscopy as an effective prevention tool. He concluded that even though colonoscopies were less effective in reducing cancer risk on one side of the colon than the other, “less effective does not mean ineffective..”.

“Protection From Colorectal Cancer After Colonoscopy – A Population-Based, Case-Control Study”
Hermann Brenner, MD, MPH, Jenny Chang-Claude, PhD, Christoph M. Seiler, MD, MSc, Alexander Rickert, MD and Michael Hoffmeister, PhD
Annals of Internal Medicine January 3, 2011 vol. 154 no. 1 22-30

Written by Christian Nordqvist