SCREENING COLONOSCOPY DECREASES COLORECTAL CANCER RELATED DEATH

April 13, 2010 — Colonoscopy has been established as an effective method of screening for colorectal cancer, and now a study has found that it is associated with a reduction in disease-related mortality.

In the study, published online March 2 in the American Journal of Gastroenterology, researchers found that for every 1% increase in the complete colonoscopy rate, the hazard of colorectal-cancer-associated death decreased by 3%.

"We found that living in a region with higher colonoscopy rates was associated with a reduced risk of death from colorectal cancer," said lead author Linda Rabeneck, MD, MPH, professor of medicine at the University of Toronto in Ontario.

"The colonoscopies in our study were not only done for screening, but for other reasons, such as diagnosis," she told Medscape Oncology. "Overall, we can say at a population level that the increase in colonoscopy use has been associated with a benefit."

However, an expert contacted for independent comment cautioned that the findings need to be interpreted with care. There was an association between an increased colonoscopy rate and a decreased colorectal cancer mortality rate, but this does not necessarily mean that one was the result of the other, said Charles Kahi, MD, assistant professor of clinical medicine at Indiana University School of Medicine in Indianapolis.

Colonoscopy Is the Gold Standard

Colonoscopy has become the gold standard for detecting and removing adenomas, the authors note, and colonoscopic polypectomy is associated with a decrease in the incidence of colorectal cancer. The use of colonoscopy in the United States and Canada has increased during the past 2 decades, but it remains unclear whether increased use is associated with clinical benefits at the population level.

This was the question that Dr. Rabeneck and colleagues wanted to answer. They used population data from the Canadian Institute for Health Information discharge abstract and same-day surgery databases, the Ontario Health Insurance Plan database, the Registered Persons Database, and the Ontario Cancer Registry.

A cohort of 2,412,077 people between the ages of 50 and 90 years on January 1, 1993 was identified. Each person was assigned to 1 of 13 regions, based on his/her residence, and all participants were followed until December 31, 2006. Every year for each region, the rate of colonoscopies performed on people within this age group was calculated. The authors used the multivariable Cox proportional hazards models to evaluate the association between colonoscopy rate and colorectal-cancer-associated death, adjusting for confounders such as age, sex, comorbidity, income, and location of residence (urban vs rural).

The mean age of the participants was 64 years, and approximately half (53.7%) were female. During the 14-year follow-up, 62,819 study participants (2.6 %) were diagnosed with colorectal cancer, and 23,743 (0.98%) died from the disease. Of the entire cohort, 773,677 (32.1 %) participants died from all causes.

Rates Increased, Mortality Declined

From 1993 to 2006, rates of colonoscopy increased in all regions, and the researchers noted that this increased rate was inversely associated with colorectal-cancer-related deaths. The hazard ratio of 0.970 (95 % confidence interval, 0.949 - 0.991) indicated that for every increase in colonoscopy rate of 1% in the region the participant resided, the hazard of death decreased by 3%.

Colorectal-related mortality was lower among younger adults (50 to 69 years), and within each age group, the rates were lower for women than for men. The researchers also found that increased age, lower income, and a rural residence were associated with a higher risk for death from colorectal cancer; being female was associated with a lower risk. After adjustment for these confounders, an increased complete colonoscopy rate was still associated with a decreased risk for colorectal-cancer-associated mortality.

There are several interventions that have been shown to increase screening rates, Dr. Rabeneck pointed out. "One of the most important is the recommendation of the primary care provider or family physician. This is true not just for colorectal cancer screening, but for other cancer screenings as well," she said.

Removing barriers, such as lack of insurance, is important, as is having a social marketing or public awareness campaign, she added. "That is part of the reason breast cancer screening rates are higher than rates of colorectal cancer screening," she said. "For colorectal [cancer screening], we have not yet achieved such a high level of public awareness."

Findings Need Careful Interpretation

Although this is a very nicely done study by an expert group, the findings have to be interpreted within the context of the study, said Dr. Kahi, who was approached by Medscape Oncology for independent comment.

"This is a large-scale epidemiological study, and the authors found that increased colonoscopy use was associated with decreased colorectal mortality at the population level," he summarized.

However, there are some issues that preclude making additional valid conclusions, said Dr. Kahi. "First, this is a large-scale epidemiological study, and it is often hard to translate the findings of such studies into clinical decisions for individual patients, or even to compare the results with those of clinical smaller-scale studies," he noted.

Second, the finding of an "association" does not imply causality. "In other words, increased colonoscopy use is associated with decreased mortality, but these trends may be evolving in parallel, and it does not follow necessarily that increased colonoscopy use actually caused the drop in colorectal cancer mortality," Dr. Kahi added.

"Finally, given that the study is based on administrative claims, the authors could not distinguish screening from diagnostic colonoscopy, so it is not clear if the observed association is due to the benefit of screening itself," he said.

The study received no outside funding. The researchers have disclosed no relevant financial relationships.

Am J Gastroenterol. Published online March 2, 2010. Abstract