Combination Chemotherapy in Treating Patients With Advanced Colorectal Cancer

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 which regimen of combination chemotherapy is most effective in treating advanced colorectal cancer.
PURPOSE: Randomized phase III trial to compare the effectiveness of various combination chemotherapy regimens in treating patients who have advanced, recurrent, or metastatic colorectal cancer that cannot be treated with surgery or radiation therapy.