COLONOSCOPY LEADS TO FEWER DEATHS

Colonoscopy May Be Associated With Fewer Colorectal Cancer Deaths

December 17, 2008 — Colonoscopy as performed in usual practice is associated with fewer deaths from colorectal cancer (CRC), primarily because of fewer deaths from cancer developing in the left side of the colon, according to the results of a population-based, case-control study reported in the December 15 Early Release issue of the Annals of Internal Medicine.

"Colonoscopy is advocated for screening and prevention of...CRC, but randomized trials supporting the benefit of this practice are not available," write Nancy N. Baxter, MD, PhD, from Li Ka Shing Knowledge Institute, St. Michael's Hospital; University Health Network and University of Toronto in Toronto, Ontario, Canada, and colleagues. "The accuracy of colonoscopy done in the real world is unknown but may be substantially less than that in published reports."

The goal of this study was to examine the association between colonoscopy and CRC deaths in a cohort from Ontario, Canada, of persons aged 52 to 90 years who were diagnosed with CRC from January 1996 to December 2001 and who died of CRC by December 2003. For each case patient, 5 control subjects were randomly selected, matched by age, sex, geographic location, and socioeconomic status.

Using administrative claims data, the investigators identified exposure to any colonoscopy and complete colonoscopy (to the cecum) from January 1992 to an index date 6 months before diagnosis in each case patient and the same assigned date in the matched control subjects. Conditional logistic regression controlling for comorbid conditions compared exposures in case patients (n = 10,292) and control subjects (n = 51,460), and secondary analyses determined whether associations differed by site of primary CRC, age, or sex.

Colonoscopy was performed in 719 case patients (7.0%) and 5031 control subjects (9.8%), with adjusted conditional odds ratio (OR) of having undergone any attempted colonoscopy of 0.69 for case patients vs control subjects (95% confidence interval [CI], 0.63 - 0.74; P < .001). For complete colonoscopy, adjusted conditional OR was 0.63 (95% CI, 0.57 - 0.69; P < .001).

Complete colonoscopy was strongly associated with fewer deaths from left-sided CRC (adjusted conditional OR, 0.33; 95% CI, 0.28 - 0.39). However, complete colonoscopy was not linked to fewer deaths from right-sided CRC (adjusted conditional OR, 0.99; 95% CI, 0.86 - 1.14).

"In usual practice, colonoscopy is associated with fewer deaths from CRC," the study authors write. "This association is primarily limited to deaths from cancer developing in the left side of the colon."

Limitations of this study were that screening could not be differentiated from diagnostic procedures, confounding by factors inadequately controlled for by matching or adjustment, inability to assess family history, inability to detect exposure to colonoscopy before 1991, and overall rate of colonoscopy low in case patients and control subjects.

"Although randomized, controlled trials with cancer death as the outcome are the gold standard for evaluating cancer screening, no such trial of screening colonoscopy is currently under way," the study authors conclude. "In an Ontario-wide sample, colonoscopy is associated with a reduced risk for death from CRC arising from the left colon but not from the right colon. Although improvements in the quality of screening colonoscopy may narrow this difference, differences in tumor biology may limit the potential to prevent right-sided colon cancer deaths with current endoscopic technology."

In an accompanying editorial, David F. Ransohoff, MD, from the University of North Carolina at Chapel Hill, suggests that unrealistic goals regarding prevention of CRC deaths with colonoscopy may lead to risks if they cause overuse of colonoscopy.

"Although colonoscopy is generally safe, it is still an invasive procedure with a 0.2% rate of serious complications — 10 times higher than for any other commonly used, cancer screening test," Dr. Ransohoff writes. "Colonoscopy is an effective intervention, but, as Baxter and colleagues suggest, we must realize that current evidence is indirect and does not support a claim of 90% effectiveness. Until we have better data, we can be grateful and optimistic to have a useful intervention to offer our patients, but we should be realistic and cautious when talking with them about the magnitude of both benefits and risks."