Elsevier

Gastrointestinal Endoscopy

Volume 76, Issue 2, August 2012, Pages 355-364.e1
Gastrointestinal Endoscopy

Original article
Clinical endoscopy
Effect of colonoscopy on colorectal cancer incidence and mortality: an instrumental variable analysis

https://doi.org/10.1016/j.gie.2012.03.247Get rights and content

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.

Design

Population-based retrospective cohort study.

Setting

Ontario provincial health data information.

Patients

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.

Intervention

Colonoscopy between 1996 and 2000.

Main Outcome Measurements

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.

Limitations

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

Conclusion

Increased use of colonoscopy procedures is associated with a reduction in the incidence and mortality of CRC in the population studied.

Section snippets

Overview

We first identified persons aged 50 to 74 years in Ontario who received health care from the same PCP from 1996 to 2000. We then determined whether each patient underwent a colonoscopy for any reason during this 5-year period. Because we were interested in characterizing PCPs' use of colonoscopy, we linked each participant to a PCP, and the intensity of colonoscopy use for each PCP was measured. To obtain an estimate of each PCP's inclination to use colonoscopy in apparent “screening”

Results

Of the 2,900,321 screen-eligible Ontario residents aged 50 to 74 years during the period from 1996 to 2000, 85.7% could be linked to a PCP. Of these, 73.8% had the same PCP over 5 years, and 73.1% had at least 2 years of continuous care from the same PCP. The study cohort was made up of 1,089,998 persons who were alive and free of CRC on January 1, 2001, and whose PCPs sent at least 3% of his or her linked patients for colonoscopy (Fig. 1). The mean age of patients was 62 years, and 54.9% were

Discussion

By using instrumental variable methods to estimate the effectiveness of colonoscopy in the prevention of CRC among persons aged 50 to 74 years, we found that use of colonoscopy was associated with a relative 7-year decrease in CRC incidence of 48% and a relative 5-year decrease in CRC death of 81%. Increasing the rate of colonoscopy in the population—even among people who may not have a clinical indication for colonoscopy—has the potential to make a substantial impact on CRC incidence and

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    DISCLOSURE: This work was supported by grants from the Canadian Institutes of Health Research and Colon Cancer Canada. The study was supported by the Institute for Clinical Evaluative Sciences (ICES), which is funded by an annual grant from the Ontario Ministry of Health and Long-Term Care (MOHLTC). The opinions, results, and conclusions reported in this article are those of the authors and are independent from the funding sources. No endorsement by ICES or the Ontario MOHLTC is intended or should be inferred. Nancy Baxter holds the Cancer Care Ontario Health Services Research Chair and an Early Researchers Award from the Ontario Ministry of Research and Innovation. No other financial relationships relevant to this publication were disclosed.

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