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