Screening sigmoidoscopy for colorectal cancer: further pieces in the jigsaw

Consensus is yet to be reached on the optimal approach to screening AUSTRALIANS have a 1 in 21 lifetime risk of developing colorectal cancer. 1 The incidence of the disease and mortality resulting from it can be reduced by population-based screening programs, as has been demonstrated in several large randomised controlled trials of faecal occult blood testing (FOBT). 2 The Bowel Cancer Screening Pilot Program currently under way in Queensland, South Australia and Victoria is assessing the practical application of FOBT. While screening of asymptomatic, average-risk individuals for colorectal cancer is advocated by many authorities worldwide (including the National Health and Medical Research Council [NHMRC] in Australia 1), uncertainty remains as to the screening test of choice. The numerous publications on the subject are indeed like jigsaw pieces waiting to be put together to reveal the complete picture. In addition to FOBT, the NHMRC-recommended screening options for asymptomatic, average-risk individuals include flexible sigmoidoscopy (FS), and it is timely to review its role here. Colonoscopic studies on asymptomatic people show that 60% of adenomas and cancers occur in the distal colon and are potentially detectable by sigmoidoscopy. Case–control studies have shown that sigmoidoscopy can reduce the risk of subsequent fatal distal colorectal cancer by up to 60%, translating to an approximate 30% reduction in overall colon cancer mortality. 3 Direct evidence of the magnitude of benefit from randomised controlled trials that are currently under way is awaited. A 5-yearly screening interval is recommended, based on data from these ongoing studies (which suggest that benefit from sigmoidoscopy extends up to 10 years) and on studies of repeat colonoscopy (which show that significant neoplasia is very uncommon 5 years after polypectomy or a normal examination). What are the performance characteristics of FS? The procedure is typically done in an unsedated patient after administration of an enema and takes 5–10 minutes to perform. At our institution, generally eight procedures are done by one operator over 2 hours. The instrument is advanced as far as is tolerated with reasonable comfort (mean insertion depth, 60 cm; range, 30–110 cm 4) with biopsy or removal of polyps performed at the time. The finding of any adenomatous polyp or other suspicious lesion prompts further evaluation with colonoscopy. Fifteen percent of such screenings result in referral for colonoscopy. 5 However, some have suggested that diminutive adenomas may not require follow-up — a policy that might reduce colonoscopy referrals to …