Fluorouracil and Irinotecan With or Without Leucovorin Compared With Observation in Treating Patients Who Have Undergone Surgery for Stage II Colon Cancer

OBJECTIVES: Primary * Compare 5-year disease-free survival in patients with resected stage II adenocarcinoma of the colon treated with adjuvant chemotherapy comprising fluorouracil and irinotecan with or without leucovorin calcium vs no adjuvant therapy. Secondary * Compare 8-year overall survival in patients treated with these regimens. * Compare tolerability of these regimens in these patients. * Correlate clinical, histological, and biological prognostic factors with outcome in patients treated with these regimens. OUTLINE: This is a randomized, multicenter study. Patients are stratified according to participating center, disease stage (pT3 vs pT4), pathological differentiation (poorly or undifferentiated vs well or moderately differentiated), and microsatellite instability (positive vs negative vs unknown). Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients are further randomized to receive 1 of 3 adjuvant chemotherapy regimens. * Regimen A: Patients receive irinotecan IV over 90 minutes followed by leucovorin calcium IV over 2 hours and fluorouracil IV continuously over 46 hours on days 1, 15, and 29. Treatment repeats every 42 days for up to 4 courses in the absence of disease progression or unacceptable toxicity. * Regimen B: Patients receive irinotecan IV over 30-90 minutes followed by leucovorin calcium IV over 2 hours and fluorouracil IV continuously over 24 hours on days 1, 8, 15, 22, 29, and 36. Treatment repeats every 56 days for up to 4 courses in the absence of disease progression or unacceptable toxicity. * Regimen C: Patients receive irinotecan IV over 60 minutes followed by fluorouracil IV continuously over 48 hours on days 1, 8, 15, 22, 29, and 36. Treatment repeats every 42 days for up to 4 courses in the absence of disease progression or unacceptable toxicity. * Arm II: Patients undergo observation only. Patients are followed every 6 months. PROJECTED ACCRUAL: A total of 1,976 patients (988 per treatment arm \[247 each in regimens A and B of arm I and 494 in regimen C of arm I\]) will be accrued for this study within 4.5 years.