Prevention of colorectal cancer. Costs and effectiveness of sigmoidoscopy.
There is increasing evidence that endoscopic polypectomy is a very effective means of preventing colorectal cancer. The feasibility of population-wide endoscopic screening is not established, however. The appearance of adenomatosis around the age of 60 in one-third of the population, many years prior to the manifestation of significant numbers of colorectal cancers, and the observation that the risk of developing metachronous adenomas correlates with pre-existing numbers of adenomas per colon suggest that a baseline endoscopy at 60 years with minimal follow-up may be a feasible screening strategy with a high rate of primary prevention in average risk individuals. Projections were made of the costs and benefits of various scenarios. A key element of this analysis was the assessment of probabilities to develop metachronous adenomas as a function of prior adenoma status by a mathematical approach using autopsy data. A screening strategy consisting of a baseline sigmoidoscopy at 60 years with follow-up restricted to 6% of the population was estimated to prevent 50% of colorectal cancers occurring after 60 years. A range of alternative scenarios, giving rates of primary prevention of colorectal cancer from 40 to 70%, had costs which were comparable to those of breast-cancer screening, but was far superior considering effectivity.