[Precancerous lesions of the colon and rectum].

We discussed significance of various kinds of precancerous lesions of the colon and rectum. Colonic adenoma was most important as a histogenetic background of colonic carcinoma, as it has been widely accepted. The first malignant transformation of adenoma seemed to occur at the relatively superficial layer of the central portion of adenoma in many cases. Growth rate of adenoma largely depended on cellular atypia. Six of twenty-seven patients with Peutz-Jeghers syndrome had advanced carcinoma and/or carcinoma in Peutz-Jeghers polyp. In general, malignant transformation in the polyp was higher in frequency in polyps more than 3.0 cm in the largest dimension. Significance of precancerous lesions in juvenile polyp, hyperplastic polyp, ulcerative colitis, Crohn's disease and radiation colitis was briefly presented.