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