Role of nonpolypoid neoplastic lesions in the pathogenesis of colorectal cancer

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Abstract
The aim of this study was to investigate the role of nonpolypoid neoplastic lesions of the colorectum in the pathogenesis of colorectal cancer.We retrospectively compared the incidence of cancer between polypoid and nonpolypoid lesions detected by colonoscopy during the period of 1991 to 1992.Of the 686 lesions in 336 patients included in the investigation, 644 lesions were regarded as polypoid, either sessile, semipedunculated, or pedunculated, while 42 lesions were recognized as small nonpolypoid lesions characterized by minimal elevation with depression on colonoscopy. The incidence of cancer in adenoma or pure cancer was significantly higher in the nonpolypoid lesions (19.0 percent) than in the polypoid lesions (6.8 percent, P < 0.01), especially in the lesions found in the rectum or in the sigmoid colon. In addition, all 8 nonpolypoid cancers were pure cancers, whereas 26 of the 44 polypoid cancers contained adenoma. The nonpolypoid cancers were smaller and they invaded the submucosa more frequently than did the polypoid cancers.Nonpolypoid lesions are more likely to be a precursor of advanced cancer in the colorectum than usual polyps. Colonoscopists should strive hard to detect these lesions with a view to cancer surveillance, even though they are generally found less frequently than polyps.