Age-dependent shift-to-the-right in the localization of colorectal adenomas.

The age-dependent prevalence and topographical distribution of colorectal adenomas was investigated in 1006 unselected autopsies (554 males and 452 females) in Mainz, FRG. In 200 out of 1006 autopsies (19.8%) a total of 498 adenomas of the large intestine were detected. The percentage of patients with adenomas increased continuously with age. Only 6% of all adenomas were localized in the caecum and 8% in the rectum, whereas all the other adenomas were distributed rather evenly throughout the ascending colon (23%), the transverse colon (25%), the descending colon (15%) and the sigmoid colon (23%). Analyzing the topographical distribution of adenomas for definite age groups (40-59, 60-69, 70-79 and 80-99 years of age), it became evident that the topographical distribution is not constant, but shows an age-dependent shift-to-the-right, i.e. with advancing age an increase in the relative frequency of adenomas in the proximal colonic segments (from caecum to transverse colon) and a decrease in the distal segments (from descending colon to rectum). This shift to the right, which evolves continuously from the youngest to the oldest age group, results from a disproportionate increase in the absolute number of adenomas in the proximal colonic segments when compared with the distal segments. The age-dependent shift-to-the-right of colorectal adenomas provides an important confirmation of the adenoma-carcinoma sequence, but cannot be explained by current concepts concerning the aetiology of colorectal adenomas and carcinomas.