Natural History of Colorectal Adenoma and the Effect of Endoscopic Polypectomy on Occurrence of Subsequent Cancer.

Colorectal cancer is thought to originate in colorectal adenoma and endoscopic polypectomy may prove prophylactic. To clarify the natural history of colorectal adenoma and the potential effects of endoscopic polypectomy, we retrospectively studied cohort patients undergoing full colonoscopies at 14 hospitals in Aomori Prefecture between January 1972 and December 1985. Subjects were divided into 3,574 non-adenoma controls and 1,020 adenoma patients, including 530 treated by polypectomy at initial examination. Subjects were followed up until the end of 1987 through record linkage with Aomori Colorectal Cancer Registry files to observe colorectal cancer occurrence. The ratio of observed number/expected number in the general population (O/E ratio) was 0.70 for the adenoma group and 0.36 for controls. The adenoma group was subdivided into polypectomy and non-polypectomy subgroups, with the O/E ratios of 0.39 for polypectomy patients and 0.75 for non-polypectomy patients. The O/E ratio in the adenoma group was about twice in controls, and this ratio in the nonpolypectomy subgroup was also about twice in thepolypectomy subgroup. The results suggest that colorectal adenoma provides a precancerous lesion that can be treated prophylactically by endoscopic polypectomy.