Colonoscopy is associated with significant reductions in colorectal cancer (CRC) mortality among veterans and with greater benefit for left-sided cancer than right-sided cancer, according to a study published in the Annals of Internal Medicine.

Charles J. Kahi, MD, MSc, from the Richard L. Roudebush VA Medical Center and Indiana University School of Medicine in Indianapolis, and colleagues conducted a case-control study to determine whether colonoscopy is associated with decreased CRC mortality in veterans and whether its effect differs by anatomical location of CRC. The sampling frame included veterans with inpatient and/or outpatient visits at any VA facility from 1997 to 2010. Patients were veterans who received a diagnosis of CRC when they were aged 50 years or older and died of CRC when they were aged 52 years or older. Patients were identified from January 1, 2002, to December 31, 2002, and died of CRC between January 1, 2002, and December 31, 2010.

Exposure was defined as receipt of colonoscopy between January 1, 1997, and 6 months before CRC diagnosis in case patients. Subgroup analysis was performed for patients who had undergone screening colonoscopy.

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A total of 4,964 case patients and 19,856 control patients were identified. The mean age was 70.7 years (SD, 10.0), and 99.3% were male. A total of 668 case patients and 5,250 control patients were exposed to colonoscopy; the indication was diagnostic in 68.7% and 60.9%, screening in 15.3% and 21.3%, and surveillance in 16.0% and 17.8%, respectively. Median time between colonoscopy and CRC diagnosis was 43.5 months (range, 6 to 141 months) among case patients. The proportions of patients who underwent colonoscopy for a screening indication were 8.0% from 1997 to 2001, 32.2% from 2002 to 2006, and 32.6% in 2007 or later.

Case patients were significantly less likely to have undergone any colonoscopy (OR, 0.39). Colonoscopy was associated with reduced mortality for left-sided cancer (OR, 0.28) and right-sided cancer (OR, 0.54). The results were similar for patients who had undergone screening colonoscopy (overall OR, 0.30). Sensitivity analyses that varied the interval between CRC diagnosis and colonoscopy exposure did not affect the primary findings.

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“In this study using national VA–Medicare data, colonoscopy was associated with a 61% reduction in CRC mortality among veterans,” the authors stated. “This reduction was observed for both left- and right-sided CRC, although the association was weaker for right-sided cancer (46% vs 72% mortality reduction). These trends were also observed in the screening colonoscopy subgroup.”

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Kahi CJ, Pohl H, Myers LJ, Mobarek D, Robertson DJ, Imperiale TF. Colonoscopy and colorectal cancer mortality in the Veterans Affairs Health Care System: a case–control study. Ann Intern Med. 13 March 2018. doi: 10.7326/M17-0723. [Epub ahead of print].