Leucovorin and Fluorouracil With or Without Oxaliplatin Compared to Capecitabine With or Without Oxaliplatin in Treating Patients With Metastatic Colorectal Cancer

RATIONALE: Drugs used in chemotherapy, such as leucovorin, fluorouracil, capecitabine, and oxaliplatin, 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 leucovorin and fluorouracil with or without oxaliplatin is more effective than capecitabine with or without oxaliplatin in treating patients who have metastatic colorectal cancer. PURPOSE: This randomized phase III trial is studying four different chemotherapy regimens to compare how well they work in treating patients with metastatic colorectal cancer.