Strong reduction of distal colorectal cancer incidence and mortality but no reduction of proximal colon cancer after screening colonoscopy: prospective cohort study
Authors: Guo Feng , Chen Chen , Holleczek Bernd , Schöttker Ben , Hoffmeister Michael , Brenner Hermann 
Published: March 2020

Background

A claimed advantage of colonoscopy over sigmoidoscopy in colorectal cancer (CRC) screening is prevention of CRC not only in the distal colon and rectum but also in the proximal colon. We aimed to assess the association of screening colonoscopy use with overall and site-specific CRC incidence and associated mortality.

Methods

Information on use of screening colonoscopy as well as potential confounding factors was obtained at baseline in 2000-2002, updated at 2-, 5-, and 8-year follow-up from 9207 participants aged 50-75 years without history of CRC in a statewide cohort study in Saarland, Germany. Covariate-adjusted associations of screening colonoscopy with CRC incidence and mortality, which were obtained through record linkage with the Saarland Cancer Registry and mortality statistics up to 2016, were assessed by Cox proportional hazards models with time-varying exposure information.

Findings

During a median follow-up of 15·3 years, 227 participants were diagnosed with CRC and 81 died from CRC. Screening colonoscopy was associated with strongly reduced overall CRC incidence (adjusted hazard ratio, aHR 0·54, 95% confidence interval, CI 0·41-0·72) and mortality (aHR 0·39, 95% CI 0·24-0·63). However, strong incidence and mortality reduction was seen for distal CRC (aHRs 0·44, 95% CI 0·30-0·63, and 0·35, 95% CI 0·19-0·66, respectively) only, but not for proximal CRC (aHRs 0·99, 95% CI 0·58-1·68, and 0·72, 95% CI 0·29-1·81, respectively).

Conclusion

In this large prospective cohort study from Germany, screening colonoscopy was associated with strong reduction in total and distal CRC incidence and mortality, but no reduction was seen for cancer incidence and mortality in the proximal colon.

Research in context

Evidence before this study

Multiple randomized controlled trials have demonstrated that screening with flexible sigmoidoscopy can substantially reduce incidence and mortality from cancer in the distal colon and rectum.

Evidence on the impact of screening colonoscopy on colorectal cancer incidence and mortality from randomized trials is lacking, and evidence from prospective cohort studies is very limited.

In particular, it is highly uncertain to what extent screening colonoscopy can additionally reduce incidence and mortality from cancer in the proximal colon.

Added value of this study

This population-based, prospective statewide cohort study from Saarland/Germany with repeat updates of exposure information demonstrates major reduction of total and distal CRC incidence and mortality among people who underwent screening colonoscopy.

However, no reduction of incidence and mortality from cancer in the proximal colon was observed.

These results challenge the expectation of incremental effectiveness of colonoscopy screening over screening by flexible sigmoidoscopy in preventing colorectal cancer.

Implications of all the available evidence

Our results may impact on recommendations, offers and use of colonoscopy versus flexible sigmoidoscopy for colorectal cancer screening.