Effect of colonoscopy on colorectal cancer incidence and mortality: an instrumental variable analysis.
BACKGROUND
Using population-based health services information to estimate the effectiveness of colonoscopy on colorectal cancer (CRC) outcomes is prone to selection bias.


OBJECTIVE
To determine the effect of colonoscopy on CRC incidence and mortality.


METHODS
Population-based retrospective cohort study.


METHODS
Ontario provincial health data information.


METHODS
This study involved average-risk persons aged 50 to 74 years from 1996 to 2000 who were alive and free of CRC on January 1, 2001.


METHODS
Colonoscopy between 1996 and 2000.


METHODS
CRC incidence and mortality from 2001 to 2007.


RESULTS
The study cohort contained 1,089,998 persons, 7.9% of whom had undergone a colonoscopy between 1996 and 2000. Using primary care physician rate of discretionary colonoscopy as an instrumental variable, the receipt of colonoscopy was associated with a 0.60% (95% confidence interval [CI], 0.31%-0.78%) absolute reduction in the 7-year colorectal cancer incidence and a 0.17% (95% CI, 0.14%-0.21%) absolute reduction in the 5-year risk of death caused by CRC. This corresponds to a 48% relative decrease in CRC incidence (risk ratio [RR] 0.52; 95% CI, 0.34-0.76) and 81% decrease in mortality caused by CRC (RR 0.19, 95% CI, 0.07-0.47). In subgroup analyses, the reduction in the risk of death due to CRC was larger in women than men. The reduction in CRC incidence was larger for complete colonoscopies and for left-sided cancers.


CONCLUSIONS
Instrumental variable methods estimate only the marginal effect on the population studied.


CONCLUSIONS
Increased use of colonoscopy procedures is associated with a reduction in the incidence and mortality of CRC in the population studied.
Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
Binu J
BJ
Jacob
Rahim
R
Moineddin
Rinku
R
Sutradhar
Nancy N
NN
Baxter
David R
DR
Urbach
D000368:Aged; D015331:Cohort Studies; D003113:Colonoscopy / Q000706:statistics & numerical data; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000401:mortality / Q000517:prevention & control; D055088:Early Detection of Cancer / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D017063:Outcome Assessment, Health Care; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data; D012042:Registries; D012189:Retrospective Studies; D016019:Survival Analysis