In November 2015, we published a systematic review that evaluated the existing evidence for screening adults at average risk for colorectal cancer in the context of an organized, population-based screening program.
The main objectives of Colorectal Cancer Screening in Average Risk Populations: Evidence Summary, were to identify:
- benefits and harms of screening
- optimal primary colorectal cancer screening tests
- appropriate ages to start and end screening
- intervals for screening recall
The evidence summary reported what is known about the clinical effectiveness and safety of colorectal cancer screening tests. This was the first step in developing these average risk screening recommendations for ColonCancerCheck.
The evidence summary was developed by our internationally recognized Program in Evidence-Based Care, with the assistance of a guideline working group formed for that purpose. (Learn more about the Program in Evidence-Based Care.)
The next phase was to consider additional information such as cost-effectiveness, existing program design, public acceptability and feasibility from an organizational and economic perspective. A large, multidisciplinary expert panel met to discuss the evidence and provide implementation considerations. Panel members included:
- representatives from national and international screening programs
- primary care physicians
- general surgeons
- pathologists and laboratory medicine professionals
- nurse endoscopists
- members of the public
The final phase brought the clinical evidence and implementation considerations provided by the expert panel together as key inputs in the development of the updated screening recommendations.
Alignment with the Canadian Task Force on Preventive Health Care
The ColonCancerCheck screening recommendations align closely with the recommendations released by the Canadian Task Force on Preventive Health Care in February 2016. Both organizations recommend screening people at average risk of colorectal cancer with fecal occult blood testing or flexible sigmoidoscopy.
The task force recommends against colonoscopy to screen people at average risk. ColonCancerCheck found insufficient high-quality, direct evidence to support screening people at average risk of colorectal cancer with colonoscopy, and therefore ColonCancerCheck did not include colonoscopy in its recommendations.
Evidence from flexible sigmoidoscopy research can be used to inform the assessment of colonoscopy in this population. It is anticipated that the benefits of screening with colonoscopy would be at least equivalent to those observed for screening with flexible sigmoidoscopy; the magnitude of additional benefits and harms, if any, is unknown.
Therefore, due to a lack information on the balance of benefits and harms, colonoscopy is not included in the ColonCancerCheck screening recommendations.
Flexible Sigmoidoscopy – Screening Interval Extended to 10 Years
The ColonCancerCheck screening recommendations released in 2016 are based on a systematic review of the clinical evidence, additional information (e.g., cost-effectiveness), existing program design, public acceptability and feasibility, and advice from a multidisciplinary expert panel. The 10-year interval for flexible sigmoidoscopy screening was based on several key considerations.
Three randomized controlled trials were identified that evaluated colorectal cancer screening using once-in-a-lifetime flexible sigmoidoscopy. The observation window was at least 10 years for all 3 trials; the reported benefits (reduced mortality and incidence) were measured at this time (see table 1).
Table 1. Flexible Sigmoidoscopy Randomized Control Trial Data
|Study Name: Author, Year
||Sample Size FS
||Sample Size Control
||Median Length of Follow-Up (Years)
||Relative Risk (95% CI)
|Relative Risk (95% CI)
Abbreviations: CI: confidence interval; CRC: colorectal cancer; NORCCAP: Norwegian Colorectal Cancer Prevention; SCORE: Screening for Colon Rectum; UKFSST: UK Flexible Sigmoidoscopy Screening Trial
The colorectal cancer adenoma–carcinoma progression sequence is believed to take more than 10 years, especially for cancers on the left side of the colon. Therefore, re-screening with flexible sigmoidoscopy after 5 years is expected to have limited utility for left-sided cancer and adenoma detection.
This recommendation aligns with the 2016 colorectal cancer screening guidelines from the Canadian Task Force on Preventive Health Care and the draft colorectal cancer screening recommendations from the U.S. Preventive Services Taskforce released for public comment in the fall of 2015.