Risks, costs, and compliance limit colorectal adenoma surveillance: lessons from a randomised trial

Background and aims-In the USA and many other countries, endoscopic surveil lance of colorectal adenoma patients is now widely practised. However, the optimal frequency and mode of such surveillance are not yet established. Th e aim of this trial was to compare surveillance at one, two, or five year i ntervals using either flexible sigmoidoscopy or colonoscopy. Methods-Analysis of a randomised trial of flexible sigmoidoscopy and colono scopy over one, two, or five years after stratification for "high" or "low" risk of recurrent adenomas. The trial started in 1984. Results-A total of 776 patients were stratified into "high" (n=307) and "lo w" (n=469) recurrence risk groups and randomised to flexible sigmoidoscopy or colonoscopy at varying intervals. Only 81 recurrent adenomas (30/81 were >1 cm in diameter) were detected in the 2307 person years of follow up wit hin the surveillance study. Adenoma recurrence was significantly higher in the high risk group (relative rate 1.82; 95% confidence interval 1.2-2.9) b ut recurrence rates per 1000 person years were low and not significantly di fferent in those surveyed by colonoscopy or flexible sigmoidoscopy. Loss to follow up was greatest in those having an annual examination compared with two or five yearly surveillance examinations. Despite surveillance, invasi ve cancer developed in four patients compared with an expected value of 9.1 2 for the general population in England (p=0.10); of these four patients wh o developed cancers, only one was detected by surveillance examination. Conclusions-Adenoma recurrence rates were much lower than expected in both high and low risk groups. This suggests that endoscopic surveillance should be targeted at high risk groups. A surveillance interval of five years was as effective as shorter intervals in terms of cancer prevention, and was a ssociated with similar compliance to two yearly examinations.