A Multicenter Study of Colorectal Adenomas Rationale, Objectives, Methods and Characteristics of the Study Cohort

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Abstract
Background and Aims: The Multicenter Study of Colorectal Adenomas (SMAC) is a retrospective-prospective cohort study involving four Gastrointestinal Endoscopy Units in Italy. The main aim of the study is to evaluate the relationship between clinical and pathologic information at index colonoscopy and subsequent incidence of adenoma and colorectal carcinoma. We report the rationale, objectives and methods of the study, including patient characteristics at initial presentation. Methods: All patients were consecutively identified from the endoscopy registries of the four Centres from January 1, 1985 to December 31, 1992. Inclusion criteria were: age 18-69 years, endoscopy performed with adequate toilette at least up to the rectosigmoid junction, and removal of all detectable polyps. Exclusion criteria were: familial adenomatous polyposis, inflammatory bowel diseases, adenocarcinoma in adenoma with infiltrated margins, previous invasive cancer at any site, colon resection and geographic inaccessibility. Results: Out of 20,071 patients who underwent endoscopy at the four Centres, 11,959 fulfilled the eligibility criteria (5,892 males and 6,067 females, mean age = 51.1 ± 11.6 years). The main reasons for exclusion were age (n = 4,020) and previous or present colorectal cancer (n = 2,389). Symptoms were the most common reason for referral (72.3%), while post-polypectomy follow-up and positive fecal occult blood accounted for most of the remaining cases. A pancolonoscopy was performed in 3,088 patients (25.8%), while a left-sided endoscopy was performed in 7,887 (66%). A total number of 4,810 polyps were removed from 2,699 patients (2,994 adenomas, 1,580 hyperplastic polyps and 236 polyps lost after resection). A significant association (p < 0.001) between age and the endoscopic findings was observed. The subjects without polyps (n = 9,198) had the lowest age (mean = 49.9; 95%CL = 49.6 - 50.1) followed by the patients with hyperplastic polyps (n = 661; mean age = 52.3; 95%CL = 51.5-53.1), and the patients with adenomas (n = 1,732; mean age = 56.2; 95%CL = 55.8 - 56.6), and the patients with hyperplastic polyps and adenomas (n = 306; mean age = 57.2; 95%CL = 56.3 - 58.2). Polyps were diagnosed more frequently in males than in females (28.6% versus 17.0%; p < 0.0001). Conclusion: This study provides some insights in the natural history of colorectal cancer and stresses the need to develop adequate strategies in the follow-up of subjects after either positive or negative colonoscopy.