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

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Combining more than one drug may kill more tumor cells. It is not yet known whether chemotherapy is more effective than observation in patients who have had surgery to remove colorectal cancer.
PURPOSE: This randomized phase III trial is studying leucovorin and fluorouracil to see how well they work compared to observation in treating patients with colorectal cancer that has been surgically removed.