title: Association of colonoscopy and death from colorectal cancer.
abstract: BACKGROUND
  Colonoscopy is advocated for screening and prevention of colorectal cancer (CRC), but randomized trials supporting the benefit of this practice are not available.
  
  
  OBJECTIVE
  To evaluate the association between colonoscopy and CRC deaths.
  
  
  METHODS
  Population-based, case-control study.
  
  
  METHODS
  Ontario, Canada.
  
  
  METHODS
  Persons age 52 to 90 years who received a CRC diagnosis from January 1996 to December 2001 and died of CRC by December 2003. Five controls matched by age, sex, geographic location, and socioeconomic status were randomly selected for each case patient.
  
  
  METHODS
  Administrative claims data were used to detect 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 matched controls. Exposures in case patients and controls were compared by using conditional logistic regression to control for comorbid conditions. Secondary analyses were done to see whether associations differed by site of primary CRC, age, or sex.
  
  
  RESULTS
  10 292 case patients and 51 460 controls were identified; 719 case patients (7.0%) and 5031 controls (9.8%) had undergone colonoscopy. Compared with controls, case patients were less likely to have undergone any attempted colonoscopy (adjusted conditional odds ratio [OR], 0.69 [95% CI, 0.63 to 0.74; P < 0.001]) or complete colonoscopy (adjusted conditional OR, 0.63 [CI, 0.57 to 0.69; P < 0.001]). Complete colonoscopy was strongly associated with fewer deaths from left-sided CRC (adjusted conditional OR, 0.33 [CI, 0.28 to 0.39]) but not from right-sided CRC (adjusted conditional OR, 0.99 [CI, 0.86 to 1.14]).
  
  
  CONCLUSIONS
  Screening could not be differentiated from diagnostic procedures.
  
  
  CONCLUSIONS
  In usual practice, colonoscopy is associated with fewer deaths from CRC. This association is primarily limited to deaths from cancer developing in the left side of the colon.
authors.affiliation: Li Ka Shing Knowledge Institute, St Michael's Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada. baxtern@smh.toronto.on.ca
authors.forename: Nancy N
authors.initials: NN
authors.lastname: Baxter
authors.forename: Meredith A
authors.initials: MA
authors.lastname: Goldwasser
authors.forename: Lawrence F
authors.initials: LF
authors.lastname: Paszat
authors.forename: Refik
authors.initials: R
authors.lastname: Saskin
authors.forename: David R
authors.initials: DR
authors.lastname: Urbach
authors.forename: Linda
authors.initials: L
authors.lastname: Rabeneck
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D003106:Colon / Q000473:pathology; D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000175:diagnosis / Q000401:mortality* / Q000517:prevention & control*; D015897:Comorbidity; D055088:Early Detection of Cancer; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D012044:Regression Analysis