Research in context
Evidence before the study
Articles on clinical trials for colorectal cancer screening were obtained from a 2016 evidence review published by the US Preventive Services Task Force (USPSTF) and by searching PubMed from Jan 1, 1995, to June 30, 2018. Most relevant to our analysis were the recent extended results from previous randomised trials of flexible sigmoidoscopy from the UK and Norway, as well as the original follow-ups of those studies and of the Prostate, Lung, Colorectal, and Ovarian (PLCO) screening trial. All three of the trials found significant reductions in colorectal cancer incidence and mortality during the original follow-up periods. The UK trial found continued risk reduction with extended follow-up but the reduction in NORCCAP was limited to men.
Added value of this study
The studies conducted in the UK and Norway included a single screening test while the PLCO included a follow-up test. It is unknown if there is a greater reduction in risk with the follow-up test. It is also important to assess if the risk reductions are consistent across populations with different health-care systems and follow-up experiences. The PLCO provides results comparing an intervention flexible sigmoidoscopy group with a usual care group, which includes a higher use of screening with colonoscopy in the general population than the European trials. The results of the extended analysis indicate that the reductions in risk from flexible sigmoidoscopy screening can be sustained long term and may differ by age group and sex.
Implications of all the available evidence
The results from this study, in combination with the other screening trials, can help inform future colorectal cancer screening guidelines.