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 with a family history of colorectal cancer but who are not diagnosed with HNPCC are allowed * No more than 1 prior segmental colon resection PATIENT CHARACTERISTICS: Age * 40 to 80 Performance status * SWOG 0-1 Life expectancy * Not specified Hematopoietic * Hemoglobin \> 11 g/dL * WBC 3,000 - 11,000/mm\^3 Hepatic * AST and ALT \< 2 times upper limit of normal * Bilirubin \< 2.0 mg/dL Renal * Creatinine \< 1.9 mg/dL Cardiovascular * No unstable\* cardiac disease despite medication (e.g., diuretics or digitalis) * No uncontrolled hypertension (i.e., systolic blood pressure ≥ 170 mm Hg and/or diastolic blood pressure ≥ 110 mm Hg) despite medication NOTE: \*Unstable defined as unable to walk across the room without chest pain or shortness of breath Other * Not pregnant or nursing * Fertile patients must use effective contraception for at least 2 months before and during study treatment * Resident of a clinical center metropolitan area or obtaining regular health care in a clinical metropolitan area for at least 6 months out of the year * Must be able to swallow pills * No unexpected weight loss of 10% or more within the past 6 months * No prior rheumatoid arthritis * No poorly controlled diabetes mellitus despite medication, defined as: * Blood sugar level ≥ 200 mg/dL on more than half of the readings taken within the past month * No invasive malignancy within the past 5 years that required medical excision, radiotherapy, or chemotherapy except basal cell or squamous cell carcinoma PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent drugs that regulate the immune system Chemotherapy * No concurrent chemotherapy Endocrine therapy * Not specified Radiotherapy * No concurrent radiotherapy Surgery * See Disease Characteristics Other * Prior enrollment in another adenoma prevention study allowed * Concurrent routine aspirin (≤ 81 mg/day) allowed * No regular use of non-steroidal anti-inflammatory drugs (NSAIDs) * No concurrent enrollment in another research study using pharmacological cancer drugs, a cyclo-oxygenase-2 inhibitor, or selenium * No other concurrent selenium unless dosage is ≤ 50 µg/day