Pathology of colorectal adenomas: a colonoscopic survey

The size, histological type, and grade of dysplasia of a large series of colorectal adenomas removed by colonoscopic polypectomy were matched against other variables such as anatomical site, age, sex, and number of adenomas per patients. Special emphasis was placed on the criteria for grading dysplasia in adenomas and the possible significance of severe dysplasia as a selective marker for increased colorectal cancer risk. The results showed that small adenomas (mostly with mild dysplasia) were evenly distributed throughout the colorectum but that adenomas showing severe dysplasia (mostly the larger tumours, greater than 10 mm diameter) were concentrated in the left colon and rectum, particularly the sigmoid part which is also the segment with the highest risk of colorectal carcinoma in high risk populations. Severe dysplasia in adenomas appears to be a selective histopathological marker for increased colorectal cancer risk. It is closely linked with increasing age and numbers of adenomas per patient, with the large adenomas and particularly those with a villous component in their histology. Severe dysplasia and multiple adenomas could be valuable markers for selecting from the total adenoma population those most deserving of close surveillance in follow-up cancer prevention programmes. Conceptually it would appear advantageous to think in term of the dysplasia-carcinoma sequence in the colorectum rather than the polyp-cancer or adenoma-carcinoma sequence. The implications of these results in the study of the aetiology of colorectal cancer are discussed.