Original article—alimentary tract
Risk of Developing Proximal Versus Distal Colorectal Cancer After a Negative Colonoscopy: A Population-Based Study

https://doi.org/10.1016/j.cgh.2008.05.016Get rights and content

Background & Aims

The incidence of colorectal cancer (CRC) overall is reduced for up to 10 years after a negative colonoscopy. The objective of this research was to determine the incidence of proximal and distal CRC after a negative complete colonoscopy.

Methods

A cohort of Ontario residents aged 50 to 80 years who had a negative complete colonoscopy between January 1, 1992, and December 31, 1997, was identified by using linked administrative databases. Cohort members had no prior history of CRC, inflammatory bowel disease, or recent colonic resection. Each individual was followed up through December 31, 2005, and the relative rate (RR) of overall CRC, distal CRC, and proximal CRC was compared with the remaining Ontario population.

Results

A cohort of 110,402 individuals with a negative complete colonoscopy was identified. The RR of CRC overall and the RR of distal CRC remained significantly lower than the Ontario population. For example, at year 14 the RR of distal CRC was 0.21 (95% confidence interval, 0.05–0.36). The RR of proximal CRC was significantly lower than the Ontario population in half of the follow-up years, mainly after 7 years of follow-up.

Conclusions

Over a 14-year follow-up period, negative complete colonoscopy was associated with a subsequent reduced incidence of CRC overall, and of incident CRC in the distal colon. However, the reduction in incidence of proximal CRC differed in magnitude and timing, and occurred in half the follow-up years, mainly after 7 years of follow-up. These results highlight an important limitation of colonoscopy in usual clinical practice.

Section snippets

Data Sources

Four data sources were used in this study.

First, the Canadian Institute for Health Information—Discharge Abstract Database (CIHI-DAD) contains information about all diagnoses and procedures for patients discharged from acute care hospitals and hospital-based, same-day surgery units for residents of Ontario since April 1, 1988. All diagnostic codes are recorded according to the International Classification of Diseases, 9th revision, clinical modification (ICD-9-CM)12 from April 1, 1988, to March

Results

From January 1, 1992, to December 31, 1997, we identified 110,402 individuals who had a negative complete colonoscopy. In the remaining Ontario population, 2,859,087 met the exclusion criteria and did not have a colonoscopy (controls). Table 1 shows the characteristics of the 2 groups. Compared with the Ontario population (controls), in the negative complete colonoscopy cohort the proportion of women was slightly greater (55.2% vs 52.1%), and the age distribution was somewhat older.

During the

Discussion

We report here that after a negative complete colonoscopy there is a sustained reduction in incident CRC overall and incident distal CRC for up to 14 years after the procedure. In the proximal colon, however, the reduction in incidence after negative complete colonoscopy differed in magnitude and timing. The reduction in incidence was observed in about half of the 14 follow-up years, and for the most part occurred after 7 years of follow-up evaluation.

It is only recently that CRC incidence

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The authors disclose no conflicts.

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