COLONOSCOPY SCREENING NOT SO GOOD FOR PROXIMAL CANCERS

October 25, 2010 (San Antonio, Texas) — Overall, colonoscopies reduce mortality rates from colorectal cancer, but the benefits appear to be limited to distal colorectal cancer, not proximal forms of the disease, according to research presented here at the American College of Gastroenterology 2010 Annual Scientific Meeting and Postgraduate Course.

Those results come from a study of 54,803 Manitoba residents from 50 to 80 years of age who received their first lower gastrointestinal endoscopy from 1987 to 2007. The findings were reported by lead author Harminder Singh, MD, from the University of Manitoba in Winnipeg.

Colorectal cancer mortality rates were 29% lower in the screened than in the general population. When analyzed by disease site, however, mortality rates from distal colorectal cancer were 47% lower than in the general population; mortality rates from proximal colorectal cancer were no different than in the general population.

Researchers analyzed data collected from patients in Manitoba's provincial physicians' billing claims database, and followed them until 2008, death, or outmigration from the province. Mortality rates were compared with those in the general population using standardized mortality ratios (SMRs).

Patients younger than 50 or older than 80 were excluded, as were those who had undergone resective colorectal surgery or who had colorectal cancer or irritable bowel syndrome.

The 29% reduction in overall colorectal mortality in the screened spatients represented a SMR of 0.71 (95% confidence interval [CI], 0.61 - 0.82).

The 47% reduction in mortality from distal colorectal cancer represented a SMR of 0.53 (95% CI, 0.42 - 0.67); for proximal colorectal cancer, the SMR was 0.94 (95% CI, 0.77 - 1.17).

The researchers also observed that the reduction in mortality from distal colorectal cancer remained significant beyond the 10-year follow-up.

According to Dr. Singh, the findings provide important insights into the specific benefits and limitations of colonoscopy screening in preventing colorectal cancer.

"There are limited data on colorectal cancer mortality after colonoscopy," he said. "A recent case–controlled study out of Ontario showed no reduction in mortality in the proximal colon after colonoscopy."

"The research presented here and the Ontario study had similar databases and are similar, but we looked over a longer time period and excluded people with prior colonoscopy and sigmoidoscopy. So we took a different approach in terms of various factors."

Douglas K. Rex, MD, professor of medicine and director of endoscopy in the Division of Gastroenterology & Hepatology at Indiana University Medical Center in Indianapolis, said the study underscores the limitations of colonoscopies in catching as many colorectal cancers as may be desired.

"It's clear from [this] study and the Ontario study that colonoscopies are not doing as well in the right colon as in the left colon. The Ontario study has been interpreted several times as indicating that colonoscopy has no benefit in the right colon," he said.

"However, these were symptomatic populations in which the prevalence of cancers in the proximal colon at the baseline colonoscopy is unknown, but likely substantially higher than an asymptomatic population. In that case, lowering the incidence of cancers to that of the general population represents a benefit from colonoscopy. The only real conclusion from these studies is that we don't do as well in the right colon as in the left."

American College of Gastroenterology (ACG) 2010 Annual Scientific Meeting and Postgraduate Course: Abstract 6. Presented October 18, 2010.