Leucovorin and Fluorouracil Compared With Observation in Treating Patients With Colorectal Cancer That Has Been Surgically Removed

OBJECTIVES: * Compare all-cause mortality in patients with resected colorectal cancer treated with adjuvant chemotherapy with L-leucovorin and fluorouracil vs observation. * Compare the recurrence rates in patients treated with this regimen vs observation. * Compare the effectiveness of a monthly 5-day schedule vs a once weekly schedule of L-leucovorin and fluorouracil in this patient population. OUTLINE: This is a randomized, open-label, multicenter study. Patients are randomized to receive adjuvant chemotherapy (arm I) or undergo observation only (arm II). * Arm I: Within 12 weeks of surgery, patients receive L-leucovorin IV followed by fluorouracil IV on days 1-5 every 4 weeks for 6 courses. Alternatively, patients may receive L-leucovorin IV followed by fluorouracil IV on day 1 weekly for 30 weeks. * Arm II: Patients undergo observation. Patients are followed annually. PROJECTED ACCRUAL: A total of 2,500 patients (1,250 per arm) will be accrued for this study.