Polyps and cancer of the large bowel: a necropsy study in Liverpool.

In a prospective necropsy study of the large bowel in 365 cases, the commonest polyp identified was the hyperplastic (metaplastic) variety, of which 86.1% of the total were located in the rectum. The other main type of polyp found, and of much greater importance because of its malignant potential, was the neoplastic adenoma. These were present, either singly or multiply, in 73 of 198 male cases (36.9%) and in 48 of 167 female cases (28.7%). Their prevalence and their tendency to be multiple rose with increasing age in both sexes. Most adenomas had a tubular growth pattern and 88.8% of these were under 1 cm in diameter. There was a fairly even distribution of adenomas throughout the large bowel but a higher proportion of adenomas over 1 cm in diameter occurred in the caecum, sigmoid colon, and rectum than at other sites. In the whole series nine adenocarcinomas were present, two of which were arising in adenomas.