Background—A multicentre randomised controlledtrial to evaluate screening by "once only" flexible sigmoidoscopy(FS) for prevention of bowel cancer is in progress.
Aims—To pilot the trial protocol examining ratesof attendance, yield of neoplasia, and adverse effects.
Subjects—A total of 3540 subjects aged 55-64years in Welwyn Garden City (WGC) and 19 706 in Leicester (LE).
Methods—Subjects responding positively to an"interest in screening" questionnaire were randomised to invitationfor screening or control arms. Small polyps were removed duringscreening. Colonoscopy was undertaken for high risk polyps (more thantwo adenomas, size at least 1 cm, villous histology, severe dysplasia,or malignancy). The remainder were discharged.
Results—In WGC and LE respectively, 59% and 61%indicated an interest in screening, of which 74% and 75% attended.Adenomas were detected in 10% and 9%, respectively, and cancers in 7 per 1000 (in both centres), 55% at Dukes's stage A. The colonoscopy referral rate was 6% in both centres. Mild, short lived bleeding occurred in 3%. One person died following surgery.
Conclusions—Compliance rates, yield of adenomas,and referral rate for colonoscopy were as expected, but cancerdetection rates were higher. Adverse effects following sigmoidoscopy or colonoscopy were mild and transient, but there was one postoperative death. A randomised trial is necessary to evaluate fully the risks andbenefits of this intervention.

Keywords:screening; colorectal cancer; adenomas; sigmoidoscopy; endoscopy; randomised trial