Missing Colorectal Cancer

It is a well-recognized fact that colonoscopy misses a proportion of polyps. In this issue of Endoscopy, Leaper et al. [1] show that colonoscopy also misses a proportion of advanced carcinomas. Most of the missed lesions were either not seen or were not recognized as malignant, despite adequate bowel preparation. This finding suggests that we can improve the detection of cancer through improved training.

Another article in this issue addresses the problem of diminutive colonic polyps [2]. Large numbers of small tubular adenomas develop as we grow older. With the use of dye spraying, adenomas have been identified in up to 50 % of asymptomatic patients attending for routine colonoscopy [3]. Hurlstone et al. [2] report that diminutive neoplastic lesions were evident in 70 % of a highly selected patient group when dye spraying and magnification were used.

Although large adenomas must develop from small precursors, the great majority of small adenomas nevertheless do not grow or become cancerous. The overall risk that a 5-mm adenoma will harbour high-grade dysplasia has previously been reported below 1 % [3] [4]. In contrast, the risk of early cancer in the study by Hurlstone et al. was much greater than 1 %. Early cancer (high-grade dysplasia, Tis or T1 cancer) was found on average in 14 % of the lesions, and the median size of the lesions was 6 - 7 mm (range 1 - 20 mm).

It may be significant that the diagnosis of high-grade dysplasia was made by a single histopathologist, who could not be blinded as to the growth pattern of the resected lesion. These findings may therefore require substantiation by other groups before we envisage a need to remove all diminutive colorectal lesions.

References

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