1 IN EVERY 13 CANCERS CAN BE MISSED WITH COLONOSCOPY

NEW YORK (Reuters Health) Oct 06 - Approximately one in every 13 colorectal cancers (CRCs) may represent a lesion missed during colonoscopy, suggests a new Canadian study.

"Several recent studies have raised questions on the effectiveness of colonoscopy as currently performed in everyday clinical practice on reducing risk of subsequent colon cancer," lead researcher Dr. Harminder Singh, of the University of Manitoba, Winnipeg, told Reuters Health in an email. "Therefore, it is important to study the factors associated with the diagnosis of colon cancer occurring after colonoscopy."

In their study, Dr. Singh and his colleagues identified nearly 5,000 individuals aged 50 to 80 who had been diagnosed with colorectal cancer between 1992 and 2008, across the entire Canadian province of Manitoba.

The team found that about 8% had been missed during colonoscopies conducted 6 months to 3 years prior to diagnosis, with a range of 4.5% of rectum/rectosigmoid cancers in men to 14.4% of transverse colon/splenic flexure cancers in women.

Women were a third more likely to have had their cancer missed, report the researchers in the September 28th online issue of the American Journal of Gastroenterology.

Further, lesions on the right side of the colon were more frequently missed, and general practice physicians left cancers undetected 60% more often than gastroenterologists.

There are three likely reasons for these "misses," noted Dr. David Lieberman of the Oregon Health and Science University in Portland. True lesions may simply have gone unidentified on the exam, or were seen but not completely removed. While rare, he also noted that it's possible an undetected cancer was actually not present at the exam, but rather grew very quickly afterwards.

No improvement in colonoscopy can do anything to avoid the latter. But the first two reasons are potentially avoidable, Dr. Lieberman told Reuters Health in an email.

The researchers call for the standardization of colonoscopy training, including credentialing and re-credentialing for clinicians performing the procedure.

"There is an urgent need to focus on and improve the outcomes of colonoscopy," Dr. Singh said.

However, Dr. Lieberman cautioned against the over-interpretation of the results. "These patients were referred for colonoscopy, most commonly due to symptoms," he said. "This is very different from a population undergoing screening."

Dr. Charles Kahi of the Indiana University School of Medicine, in Indianapolis, noted that the rate found in the new study was a bit higher than previously reported. But he added that the risk factors identified match those in earlier studies.

"The key to maximizing protection against colorectal cancer after colonoscopy is performance by an operator with excellent examination and polypectomy technique, in a well-prepped colon," Dr. Kahi told Reuters Health in an email.

"To increase their chances of an early diagnosis, it is important that all individuals undergoing colonoscopy strictly follow the instructions for bowel preparation for colonoscopy," added Dr. Singh.

Am J Gastroenterol. Posted September 28, 2010. Abstract