Association between colonoscopy and colorectal cancer mortality in a US cohort according to site of cancer and colonoscopist specialty.

PURPOSE We designed this study to evaluate the association of colonoscopy with colorectal cancer (CRC) death in the United States by site of CRC and endoscopist specialty. METHODS We designed a case-control study using Surveillance, Epidemiology, and End Results (SEER)-Medicare data. We identified patients (cases) diagnosed with CRC age 70 to 89 years from January 1998 through December 2002 who died as a result of CRC by 2007. We selected three matched controls without cancer for each case. Controls were assigned a referent date (date of diagnosis of the case). Colonoscopy performed from January 1991 through 6 months before the diagnosis/referent date was our primary exposure. We compared exposure to colonoscopy in cases and controls by using conditional logistic regression controlling for covariates, stratified by site of CRC. We determined endoscopist specialty by linkage to the American Medical Association (AMA) Masterfile. We assessed whether the association between colonoscopy and CRC death varied with endoscopist specialty. RESULTS We identified 9,458 cases (3,963 proximal [41.9%], 4,685 distal [49.5%], and 810 unknown site [8.6%]) and 27,641 controls. In all, 11.3% of cases and 23.7% of controls underwent colonoscopy more than 6 months before diagnosis. Compared with controls, cases were less likely to have undergone colonoscopy (odds ratio [OR], 0.40; 95% CI, 0.37 to 0.43); the association was stronger for distal (OR, 0.24; 95% CI, 0.21 to 0.27) than proximal (OR, 0.58; 95% CI, 0.53 to 0.64) CRC. The strength of the association varied with endoscopist specialty. CONCLUSION Colonoscopy is associated with a reduced risk of death from CRC, with the association considerably and consistently stronger for distal versus proximal CRC. The overall association was strongest if colonoscopy was performed by a gastroenterologist.