Inclusion Criteria

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