Design of a multicentre randomised trial to evaluate flexible sigmoidoscopy in colorectal cancer screening.

A randomised, controlled trial in progress in 14 United Kingdom and six Italian centres is evaluating screening for colorectal cancer using a single flexible sigmoidoscopy (FS) at around the age of 60 with removal during FS of all small adenomas, and colonoscopy for "high risk" polyps. The regimen aims to ensure that 95% of people (with either no polyps or only low risk polyps) complete the entire screening process in a single visit. This paper describes the rationale and design of the trial. Participants were patients aged between 55 and 64 on the lists of designated general practitioners (GPs) who were not excluded by their GP. A two stage recruitment procedure was employed to raise compliance rates in the intervention group. Potentially eligible persons were sent an "interest in screening" questionnaire; those who responded positively were randomised to the intervention or control groups. The trial is sufficiently large to estimate within narrow confidence intervals the magnitude of benefit and the duration of effect and optimum age for a single screen. It also examines the feasibility and acceptability of the screening regimen, and will identify training and quality assurance issues. Recruitment and screening are now complete and all baseline data have been collected. The first analysis of the effect on colorectal cancer incidence and mortality rates and suitability for a national screening programme can be expected in 2004.