Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically documented colorectal cancer that has been
curatively resected, including: Dukes' A/B1 (T1-2, N0, M0) Dukes' B2/C (T3, N0, M0 and any
T, N1, M0) disease-free more than 5 years post-resection Colonoscopy to the cecum (or
small bowel anastomosis) with removal of all polyps required within 4 months of entry
Preparation must be adequate to visualize mucosa and discern the presence of no further
polyps No familial polyposis (more than 100 polyps at time of resection) No history of
inflammatory bowel disease including ulcerative colitis or Crohn's disease

PATIENT CHARACTERISTICS: Age: 30 to under 75 Performance status: Physician's assessment of
good general health required Life expectancy: At least 5 years Hematopoietic: Not
specified Hepatic: Not specified Renal: Not specified Cardiovascular: No NYHA class III/IV
status No history of angina No history of MI No history of stroke or TIAs No peripheral
vascular disease No bleeding diathesis including hemorrhagic stroke No prophylactic
aspirin for cardiovascular disease Other: No documented peptic ulcer disease within past
15 years No aspirin sensitivity including: Aspirin-induced asthma Bronchial
hyper-reactivity Urticaria Angioedema No requirement for sodium warfarin or other
anticoagulant No frequent (greater than 36 times/year) NSAID use within the past 5 years
No recurrent arthritis or other musculoskeletal problems No narcotic or alcohol dependency
(unless there has been at least a 6-month period of abstinence) No prior or concurrent
malignancy within 5 years (including metastases) except nonmelanomatous skin cancer No
pregnant or nursing women Effective contraception required of fertile women

PRIOR CONCURRENT THERAPY: No concurrent enrollment in a colon cancer treatment trial or
other chemoprevention trial Biologic therapy: At least 6 months since immunosuppressive
therapy (i.e., azathioprine, methotrexate, cyclosporine) Chemotherapy: Prior chemotherapy
allowed for patients with Dukes' B2/C colorectal cancer No concurrent chemotherapy
Endocrine therapy: Prior non-immunosuppressive steroid treatment allowed Radiotherapy:
Prior radiotherapy allowed for patients with Dukes' B2/C colorectal cancer No concurrent
radiotherapy Surgery: Curative resection required