Background-A multicentre randomised controlled trial to evaluate screening by "once only" flexible sigmoidoscopy (FS) for prevention of bowel cancer is in progress. Aims-To pilot the trial protocol examining rates of attendance, yield of neoplasia, and adverse eVects. Subjects-A total of 3540 subjects aged 55-64 years in Welwyn Garden City (WGC) and 19 706 in Leicester (LE). Methods-Subjects responding positively to an "interest in screening" questionnaire were randomised to invitation for screening or control arms. Small polyps were removed during screening. Colonoscopy was undertaken for high risk polyps (more than two 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 cancer detection rates were higher. Adverse eVects following sigmoidoscopy or colonoscopy were mild and transient, but there was one postoperative death. A randomised trial is necessary to evaluate fully the risks and benefits of this intervention. (Gut 1998;42:560-565)

Objectives: To compare the feasibility of mass screening by flexible sigmoidoscopy with screening by faecal occult blood testing (Haemoccult) and both tests combined. Design: Patients were randomised to screening by flexible sigmoidoscopy, faecal blood testing, or both tests. The flexible sigmoidoscopy examinations were performed by a general practitioner. Setting: General practice. Subjects: 3744 patients aged 50-75 years. Main outcome measures: Uptake, positive results, detection of neoplasia, complications, and recall for diagnostic colonoscopy. Results: Uptake was significantly higher in the flexible sigmoidoscopy group (46.6%) than in the faecal blood test group (31.6%; P < 0.001) or than in the group having both tests (30.1%; P < 0.001). Telephone reminders increased uptake of sigmoidoscopy to 61.8%. In total, 1116 sigmoidoscopy examinations were performed without major complication. Polyps were found in 19.3% (95% confidence interval 17.0% to 21.6%) but only 6.8% (5.3% to 8.3%) had adenomas and 2.4% (1.5% to 3.3%) "high risk" adenomas. Cancer was detected in four subjects. The faecal blood test yielded positive results in 0.8% (0.2% to 1.4%) but missed at least one cancer and 30 cases of adenoma which were found by sigmoidoscopy in the combined group. Use of histological criteria-shown elsewhere to correlate with future risk of colorectal cancer-to select "positive" patients could reduce recall for diagnostic colonoscopy from about 20% to less than 5%. Conclusions: Some of the predicted obstacles to screening with flexible sigmoidoscopy are surmountable. Clear evidence relating to efficacy will be obtained only from a randomised controlled trial.

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