Colorectal high-grade adenomas: incidence, localization and adenoma-adenocarcinoma ratio in a retrospective and comparative population-based study of 225 consecutive cases between 1988 and 1996.

Colorectal high-grade adenomas can be regarded as precancerous lesions. This study collected epidemiological data from a defined region (Luxembourg) that can serve as reference data for designing a national screening program for early colorectal cancer detection. Nine pathologists diagnosed and reviewed slides retrospectively from 288 new colorectal and anal in situ carcinomas from the period 1988-1996 (63 were excluded for various reasons). In all, 225 new colorectal high-grade adenomas were considered. There were 129 men (57%) and 96 women (42%), and 78% of patients were aged over 60 years. Over this period we found an increase in incidence of high-grade colorectal adenomas (11 cases in 1988, 40 cases in 1996) for both sexes. The overall incidence rate was 2.9 x 100,000 in 1988 and 9.6 x 100,000 in 1996. The average annual age-standardized incidence rate for this period was 3.7+/-0.5 (95% confidence interval); the cumulative rate (0-74 years) was 0.4%. Three-fourths of the adenomas were situated in the rectum (n=78, 35%) or sigmoid colon (n=92, 41%). Histological diagnosis was provided by 160 total polypectomy specimens (71%), 30 surgical resections (13.3%), and 35 biopsy specimens (16%). Over the study period there was an increased incidence of new colorectal adenocarcinomas. There were eight times as many adenocarcinomas (n=1782) as adenomas (n=225); the distribution of anatomical sites was comparable. These epidemiological data on 225 new colorectal high-grade adenomas can be the basis for quality assurance in clinical and histological diagnostic procedures, especially in regard to the 1:8 ratio between high-grade adenomas and invasive adenocarcinomas and may provide additional data for the design of a regional or national colorectal cancer screening program.