Selenium for Prevention of Adenomatous Colorectal Polyps

DISEASE CHARACTERISTICS: * Histologically confirmed colorectal adenomatous polyps * Meets the following criteria by colonoscopy (performed within the past 6 months): * Cecum was totally visualized or reached * At least 90% visualization of colon surface area * Removed at least 1 adenomatous polyp of at least 3 mm in size during procedure (For the Advanced Adenoma Sub-study: Removal of at least 1 advanced colorectal adenomatous polyp during procedure. An adenoma is considered advanced if it is 10 mm or greater in size, and/or has villous histology and/or shows high grade dysplasia) * Removed no more than 10 adenomatous polyps of any size by endoscopy * All other neoplastic and non-neoplastic colon polyps must have been completely removed (except for diminutive \[less than 3 mm\] sessile rectal polyps) * For the sub-study, at least 1 advanced adenomatous polyp defined as 10 mm or greater in size and/or has villous histology and/or shows high grade dysplasia * No prior diagnosis of any of the following: * Colorectal cancer * Familial adenomatous polyposis * Ulcerative colitis * Crohn's disease * Hereditary non-polyposis colon cancer (HNPCC), defined as: * Histologically confirmed colorectal cancer in at least 3 relatives, 1 of whom is a first-degree relative of the other 2 * Disease occurrence in at least 2 consecutive generations * Colorectal cancer diagnosis in at least 1 family member who is less than 50 years of age * Patients wit…