Cancer Research Lab

The rate of new or missed colorectal cancer (CRC) after colonoscopy is influenced by who performs the examination and where it takes place, Canadian researchers report. Cancers are more likely to be missed with colonoscopy by an internist or family physician, and in an office setting.

Given these findings, senior investigator Dr. Linda Rabeneck said that “for the delivery of colonoscopy services in Ontario, we need to further study the practice of colonoscopy in offices and private clinics… There is something different about the practice of colonoscopy in these settings that gives rise to higher cancer miss rates, a worrisome finding.”

Dr. Rabeneck, of the University of Western Ontario, London and colleagues report their study of colorectal cancer patients in the province in the January issue of Gastroenterology.

Of 12,487 patients included, 430 (3.4%) had new or missed cancer, based on a diagnosis within 6 months to 3 years of having a colonoscopy. Reducing this period to 2 years yielded a 2.4% rate. An increase to 5 years gave a figure of 4.6%.

Further analysis showed that using the 3-year interval, right sided colorectal cancer was the most likely to be missed (5.9%). Older patient age and the presence of diverticular disease were also associated with missed cancers.

As mentioned, other independent risk factors were having colonoscopy by an internal medicine specialist or family physician and having had colonoscopy in an office.

Specifically, compared to hospital-based colonoscopy, having the procedure in an office yielded an adjusted odds ratio of new or missed colorectal cancer of 3.07 in men and 1.95 in women.

Compared to gastroenterologists, the odds ratio for missed cancers with family physicians or internists was 1.77 for men and 1.85 for women.

“For physicians performing colonoscopy, we need to advise our patients of the small chance that if they have a cancer we might miss it,” Dr. Rabeneck concluded, adding: “As we move forward with the Ontario colorectal cancer screening program, we will ensure that colonoscopy standards are implemented.”