Colorectal cancer screening in asymptomatic populations.

Colorectal cancer is the second commonest cause of cancer death in the UK. An effective national screening programme is urgently required to reduce the substantial morbidity and mortality from the disease. The success of any screening programme will depend on the screening test detecting early Dukes's A carcinomas and adenomatous polyps. Prognosis is directly related to tumour staging and a proportion of carcinomas are thought to arise from polyps. Two screening methods exist--faecal occult blood testing and sigmoidoscopy. Large trials of faecal occult blood testing show that it detects more early lesions than in patients presenting with symptoms, but whether this reduces mortality is not yet confirmed and lack of sensitivity for cancers and polyps may ultimately limits its usefulness. The role of sigmoidoscopy in screening, particularly flexible sigmoidoscopy, has not been fully investigated. Flexible sigmoidoscopy has a greater sensitivity for distal lesions than stool testing and a randomised controlled trial of its efficacy is planned in Britain. Compliance with screening is essential to ensure its cost effectiveness in both health and economic terms. Large trials of faecal occult blood testing conducted over several years achieved compliance rates in excess of 60%, although in smaller studies these are often much less. Women frequently participate more than men. There are many reasons for non-compliance including lack of appreciation of the concept of asymptomatic illness and fear of the screening tests and cancer itself. Colorectal cancer screening is relatively cheap compared with breast and cervical cancer screening. Provisional cost estimates suggest that the amount spent to detect or prevent cancer by screening is similar to the amount required to treat a symptomatic patient.