Intervention: Selenium
Trial phase: Phase 3
SMILES: [Se]
Sex: All
Age groups: Adult | Older Adult
Healthy volunteers: Accepts Healthy Volunteers
Participants at risk: 685
Group description: Participants receive oral selenium 200 mcg once daily.

Selenium: Participants will be randomized either to selenium or placebo, taking the randomized intervention for 3 to 5 years, depending on when their recommended follow up colonoscopy is scheduled.
Eligibility 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