Combination Chemotherapy in Treating Patients With Colon Cancer

OBJECTIVES: * Compare the disease-free survival of patients with completely resected stage IIB or III colon cancer treated with adjuvant chronomodulated vs standard schedule fluorouracil and leucovorin calcium with or without carboplatin. * Compare the overall survival of patients treated with these regimens. * Compare the toxicity of these regimens in these patients. * Compare the quality of life of patients treated with these regimens. * Determine the dose intensities of fluorouracil and carboplatin in these patients. OUTLINE: This is a randomized, multicenter study. Patients are stratified according to participating center and disease stage (IIB vs III). Patients are randomized to 1 of 4 treatment arms. * Arm I (standard schedule): Patients receive fluorouracil (5-FU) IV continuously and leucovorin calcium (CF) IV on days 1 and 2. * Arm II (standard + carboplatin schedule): Patients receive 5-FU and CF as in arm I plus carboplatin IV on day 1. * Arm III (chronomodulated schedule): Patients receive 5-FU IV continuously and CF IV continuously on days 1-4. * Arm IV (chronomodulated + carboplatin schedule): Patients receive 5-FU and CF as in arm III plus carboplatin IV continuously on days 1-4. Quality of life is assessed. Treatment in all arms repeats every 14 days for up to 9 courses in the absence of disease progression or unacceptable toxicity. PROJECTED ACCRUAL: A total of 660-800 patients will be accrued for this study.