Combination Chemotherapy After Surgery in Treating Patients With High-Risk Stage II or Stage III Colorectal Cancer

RATIONALE: Drugs used in chemotherapy, such as oxaliplatin, fluorouracil, and capecitabine, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. It is not yet known which combination chemotherapy regimen is more effective in treating patients who have undergone surgery for high-risk colorectal cancer. PURPOSE: This randomized phase III trial is studying chemotherapy given after surgery in treating patients with high-risk stage II or stage III colorectal cancer.