Shedding Light on Research Examining the Effectiveness of Colonoscopy for Colorectal Cancer

The U.S. Preventive Services Task Force and the American Cancer Society have recommended routine cancer screening for colorectal cancer for several decades, with colonoscopy being the predominant form of screening for colorectal cancer in the United States. Despite questions raised by a recent Nordic-European Initiative on Colorectal Cancer (NordICC) study regarding the relative value of colonoscopy, CPRIT recommends that adults continue following established guidelines to undergo regular colorectal cancer screening, including colonoscopy, beginning at age 45.

The NordICC study results, published in the New England Journal of Medicine (Bretthauer M. et al., New Engl J Med DOI: 10.1056/NEJMoa2208375), are both surprising and disappointing.  Although the study of nearly 85,000 men and women found that colonoscopy reduced the risk of colorectal cancer over a 10 year period by 18%, the reduction in the risk of death from colorectal cancer was not significant between the group receiving colonoscopy (0.28%) vs. those receiving usual care (0.31%). 

Some issues unique to this screening study may help explain these findings. 

• Screening can be effective only if it is performed. Fewer than 12,000 of 28,000 people (42%) invited to undergo screening in this study had a colonoscopy.  In other words, almost 60% chose not to be screened, which is much higher than the “no-screening rates” published in other trials.  In adjusted analyses to estimate the effect of screening if all participants who were invited to undergo screening had undergone the procedure, colonoscopy was estimated to reduce the risk of cancer by 31%, and the risk of death from colorectal cancer death by 50% - results that would be considered impactful.
• The benefits of screening colonoscopy take time to be realized. Participants in this study underwent colonoscopy only once, and there was no clear data on follow-up. This is critical because in people with polyps, follow-up is needed to treat additional polyps.
• Colorectal cancer generally develops over a long period of time. This study screened patients screened over a 5-year period (2009-2014); thus, many patients were followed for fewer than 10 years. The timeframe from the development of polyps to progression to cancer to mortality is almost always greater than this interval, indicating that a much longer follow-up period is required to provide full results.  In this regard, we have learned from other screening studies – for example, prostate cancer screening – that the data look much better with longer follow-up time.
• Colonoscopy is highly dependent on the operator performing the procedure, and medical personnel perform the procedure somewhat differently around the world. A previous report from the NordICC trial reported that many of the endoscopists had a lower rate of detection of adenomas (polyps) than the minimum recommended threshold for the procedure. 

Although the results reported by Bretthauer et al. may dampen enthusiasm for colorectal cancer screening in the near term, it’s important to remember that longer-term follow-up of participants in this study, and the results of other ongoing trials will help us to understand more fully the benefits of this screening test.  Additionally, current recommendations are based, in part, on the positive results already obtained for many cohort colonoscopy studies.  

The American Cancer Society recommends that adults undergo colorectal cancer screening, including colonoscopy, beginning at age 45.  In addition, healthy lifestyle choices related to diet, exercise, sun safety, tobacco, and alcohol use, can help lower your cancer risk.

Early detection of cancer saves lives. Regular screening gives you the best chance of finding cancer early when it can be more easily treated.

For now, it is essential to continue to receive routine cancer screening.