Clinical significance of small polyps found during screening with flexible sigmoidoscopy

In deciding how to interpret the significance and management of small distal adenomatous polyps found on FS, one must first decide on the goal of a screening program. If the goal is maximal reduction of CRC risk, regardless of cost, there is little argument that screening colonoscopy is the most effective approach. Unfortunately cost and cost-effectiveness are important considerations when administering a screening program with a fixed budget. Although comparing the cost-effectiveness of different strategies is beyond the scope of this article, rigorous comparisons by other authors have suggested that a sigmoidoscopy-based approach is more cost-effective than a colonoscopy-based approach. The most cost-effective approach may change, however, if the frequency of screening and surveillance can be reduced without significantly impacting effectiveness. Other authors using assumptions including low compliance rates for regular FOBT or FS have determined that colonoscopy every 10 years is the most cost-effective approach. Multiple studies support the recommendation that villous polyps regardless of size and adenomatous polyps greater than 1 cm found on FS are important markers for the presence of advanced polyps and cancer in the proximal colon. These patients should undergo colonoscopy. If one assumes that a sigmoidoscopy-based approach is reasonable, and accepts that such an approach always misses a small number of proximal lesions, how should one manage patients with a small adenomatous polyp on FS? In aggregate, the studies discussed previously suggest that patients with no distal polyps, distal hyperplastic polyps, or a single small distal tubular adenoma have a similar and low risk of advanced proximal adenomas of the colon. There are some studies, however, that do not support this. With the exception of the study by Read et al, these studies included patients at elevated risk of CRC because of a family history, or inclusion of patients with positive FOBT (or not tested). The study by Read et al also included patients with distal villous adenomas in their low-risk group. Because a sigmoidoscopy-based strategy typically excludes patients at elevated risk, these results may not be applicable to low-risk patients undergoing sigmoidoscopy. Given these caveats, what can one conclude about the predictive value of a small tubular adenoma found on FS? These studies suggest that the risk of proximal advanced polyps is similar or slightly increased in patients with a distal adenoma than those with a negative FS. The risk of finding an advanced adenoma seems to be 0% to 4% regardless of the findings of no polyps, hyperplastic polyps, or small tubular adenomatous polyps on FS in low-risk patients. A small portion of patients with hyperplastic polyps found on FS have advanced proximal adenomas. If a hyperplastic polyp on FS is not an indication for colonoscopy and the risk of proximal advanced adenomas is similar in patients with only a small distal adenoma, it is inconsistent to recommend colonoscopy for a small distal tubular adenoma and not a hyperplastic polyp. Based on the studies of asymptomatic patients with no family history and negative FOBT, the authors believe it is reasonable to defer colonoscopy if no polyp, a hyperplastic, or a small tubular adenoma is found at sigmoidoscopy in low-risk patients. If the patient or physician is unwilling to accept a small (0% to 4%) chance of missing an advanced proximal lesion, then a sigmoidoscopy-based approach (regardless of the threshold to go on to colonoscopy) is not appropriate. Screening FS remains an effective examination to screen for CRC in asymptomatic patients. There is no question that colonoscopy clearly detects more lesions than FS. It remains to be seen if the increase in costs and risks justifies the improved detection rate of colonic polyps. Given manpower issues that face us today, and examining the question from a population perspective, reserving colonoscopy for only those patients with an advanced distal polyp on FS gives the biggest yield.