While colonoscopy is the gold standard for screening for colon cancer, it’s not 100-percent reliable for spotting cancers in the right side of the bowel, Canadian researchers report.

They found that tumors in the right-side colon - that is, the segment furthest away from the anus - escaped detection in approximately 4 percent of patients who underwent colonoscopy in a standard clinical setting.

Therefore, physicians who perform colonoscopies should inform their patients that “there is a small chance…that cancer might be missed,” senior investigator Dr. Linda Rabeneck told Reuters Health.

Rabeneck of Sunnybrook and Women’s College Health Sciences Centre, Toronto, and colleagues note in the medical journal Gastroenterology that “miss rates” for academic and other specialized colonoscopy centers are known. This is not the case for usual clinical practice.

To investigate, the researchers examined data on 4920 Ontario residents with a new diagnosis of right-sided colon cancer who were hospitalized for surgical removal of the tumor.

Cancer was detected by colonoscopy in 96 percent. However, in 105 patients (4 percent) who had had colonoscopy between 6 to 36 months before admission, the findings appeared to be normal.

These results are similar to those of a study of Indiana hospitals that showed a 5 percent miss rate, the researchers note. However, a Western Australian teaching hospital study indicated a rate of 0.5 percent. This, the team suggests, may be due to a variety of factors ranging from skill of the endoscopist to “incomplete ascertainment of the outcome.”

Summing up, Rabeneck also stressed that patients should realize the importance of following bowel-clearing instructions before colonoscopy “to avoid the chance of retained material, which makes it harder to find any abnormality that might be there.”

SOURCE: Gastroenterology, August 2004.