No abstract

Colorectal cancer incidence after adenoma removal has been studied in selected populations of adenoma patients. Our study estimates the trend in colorectal cancer incidence after adenoma removal in actual clinical practice. From PALGA, a nationwide network and registry of histo-and cytopathology in the Netherlands, we extracted data of all patients diagnosed with colorectal adenomas between 1 January 1988 and 1 October 1998. The data were used to calculate population-based colorectal cancer incidence rates after adenoma removal. A total of 78,473 adenoma patients were followed for a mean of 4.5 years after the first adenoma removal. The colorectal cancer incidence ratio compared with the general population matched by age and gender was 38.4 (37.3-39.5) in the first year after adenoma removal and 1.5 (95% confidence interval (CI): 1.4 -1.6) after Year 1. The incidence ratio decreased from 2.8 (2.5-3.1) in Year 2 to 0.9 (0.6 -1.2) in Years 9 -11. This time trend is the opposite of the upward time trend that was expected after adenoma removal. Adenoma patients in the Netherlands are at increased risk for colorectal cancer compared to the general population. Adenomas are considered to be precursors of colorectal cancer and are effectively removed by endoscopy. A complete initial colonoscopy with polypectomy is recommended in individuals with adenomas because they are at increased risk for colorectal cancer. Furthermore, colonoscopic surveillance is recommended in these individuals to detect missed and newly developed adenomas and asymptomatic cancer. Several studies in selected centers and selected adenoma patients reported on the colorectal cancer incidence in the first years after adenoma removal. The incidence ratio compared to the general population ranged from 0.2 in the National Polyp Study, 1 and 0.4 in the study of Lund et al. 2 to 1.3 in the Funen study. 3 Patients in these studies had undergone complete initial colonoscopy or incomplete initial colonoscopy followed by (negative) barium enema. In the National Polyp Study, patients with large sessile polyps were excluded from the analysis. In unselected adenoma patients, the incidence ratio after adenoma removal may be higher than in these studies, because the compliance with and the quality of the initial colonoscopy and colonoscopic surveillance is lower than in the selected centers and because patients with large sessile polyps are included.The studies published to date have been too small to study the trend in colorectal cancer incidence according to time since polypectomy. The expectation, however, was that the effect of polypectomy would decline over time. In the first years after polypectomy, colorectal cancer incidence was expected to be low. It was thought that the incidence would later gradually increase to the level of the incidence in adenoma patients who had not previously undergone polypectomy.The aim of our study was to estimate the colorectal cancer incidence ratio in actual clinical practice in a large unselected population of adenoma patien...

Given the present, limited knowledge of the disease process of colorectal cancer, test characteristics, and costs, it may well be that the induced savings by endoscopic colorectal cancer screening completely compensate for the costs.

The data of the National Polyp Study, a large longitudinal study on surveillance of adenoma patients, is used for testing assumptions on the adenoma-carcinoma sequence. The observed adenoma and colorectal cancer incidence in the National Polyp Study were compared with the simulated outcomes of the MISCAN-COLON model of epidemiology and control of colorectal cancer for the U.S. population based on expert opinion. Variants of this model were explored in order to identify assumptions on the adenoma-carcinoma sequence that are consistent with the study observations. The high observed adenoma detection rates at surveillance and low observed colorectal cancer incidence in the National Polyp Study could only be explained by assuming a high incidence rate of adenomas accompanied by regression of adenomas. The National Polyp Study data suggest that adenoma prevalence results from a dynamic process of both formation as well as regression of adenomas. This lowers the expectations for the effects of colorectal cancer screening strategies that focus on adenoma detection.