Colorectal high-grade adenomas: incidence, localization and adenoma-adenocarcinoma ratio in a retrospective and comparative population-based study of225 consecutive cases between 1988 and 1996

Colorectal high-grade adenomas can be regarded as precancerous lesions. Thi s study collected epidemiological data from a defined region (Luxembourg) t hat can serve as reference data for designing a national screening program for early colorectal cancer detection. Nine pathologists diagnosed and revi ewed slides retrospectively from 288 new colorectal and anal in situ carcin omas 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 colorecta l adenomas (11 cases in 1988, 40 cases in 1996) for both sexes. The overall incidence rate was 2.9x100,000 in 1988 and 9.6x100,000 in 1996. The averag e 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-fou rths of the adenomas were situated in the rectum (n=78, 35%) or sigmoid col on 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 colorec tal 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 b e the basis for quality assurance in clinical and histological diagnostic p rocedures, especially in regard to the 1:8 ratio between high-grade adenoma s and invasive adenocarcinomas and may provide additional data for the desi gn of a regional or national colorectal cancer screening program.