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.

PURPOSE: Randomized phase II trial to study the effectiveness of combining fluorouracil and leucovorin with or without oxaliplatin in treating patients who have recurrent metastatic colorectal cancer.

OBJECTIVES: I. Compare the overall response rate and overall survival of patients with recurrent metastatic colorectal adenocarcinoma treated with third-line therapy comprising fluorouracil and leucovorin calcium with or without oxaliplatin. II. Compare the onset and duration of complete and partial responses and duration of disease stabilization in patients treated with these regimens. III. Compare the proportion of patients with stable disease and proportion of patients with tumor-related symptomatic improvement treated with these regimens. IV. Compare the time to disease progression and time to tumor-related symptomatic worsening in patients treated with these regimens.

OUTLINE: This is a randomized, multicenter study. Patients are randomized to one of two treatment arms. Arm I: Patients receive leucovorin calcium IV over 2 hours and fluorouracil IV over 2-4 minutes followed by fluorouracil IV continuously over 22 hours on days 1 and 2. Arm II: Patients receive oxaliplatin IV over 2 hours, leucovorin calcium IV over 2 hours, and fluorouracil IV over 2-4 minutes followed by fluorouracil IV continuously over 22 hours on day 1. On day 2, patients receive leucovorin calcium and fluorouracil as in arm I. Treatment in both arms repeats every 2 weeks for at least 1 year in the absence of disease progression. Patients are followed at day 30 and then for approximately 6 months.

PROJECTED ACCRUAL: A total of 200 patients (100 per treatment arm) will be accrued for this study.

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed adenocarcinoma of the colon or rectum Metastatic/recurrent disease not amenable to potentially curative therapy (e.g., inoperable metastatic disease) Documented sequential disease progression (by CT scan or MRI) after 2 prior chemotherapy regimens for metastatic/recurrent disease At least 1 unidimensionally measurable lesion At least 20 mm by conventional CT scan or MRI OR At least 10 mm by spiral CT scan Must have received prior fluorouracil (or capecitabine) and leucovorin calcium with or without irinotecan as first-line therapy and irinotecan with or without fluorouracil (or capecitabine) and leucovorin calcium as second-line therapy for metastatic disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 50-100% Life expectancy: Not specified Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) SGOT and SGPT no greater than 2 times ULN (6 times ULN if documented liver metastases present) Alkaline phosphatase no greater than 2 times ULN (6 times ULN if documented liver metastases present) Renal: Creatinine no greater than 1.5 times ULN Cardiovascular: No New York Heart Association class III or IV symptomatic congestive heart failure No serious cardiac arrhythmia No unstable angina No myocardial infarction within the past 6 months Pulmonary: No interstitial pneumonia No extensive and symptomatic fibrosis of the lung Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 6 months after study No known peripheral neuropathy (absence of deep tendon reflexes as the sole neurologic abnormality allowed) No diabetes or active infection No known dihydropyrimidine dehydrogenase deficiency

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior anticancer biologic therapy Chemotherapy: See Disease Characteristics No prior oxaliplatin No prior adjuvant irinotecan Prior adjuvant fluorouracil and leucovorin calcium allowed At least 3 weeks since prior chemotherapy (e.g., second-line irinotecan with or without fluorouracil (or capecitabine) and leucovorin calcium) for metastatic disease and recovered Endocrine therapy: Not specified Radiotherapy: At least 3 weeks since prior radiotherapy No prior radiotherapy to target lesion unless documented progression within the radiation portal Surgery: See Disease Characteristics At least 4 weeks since prior surgery for primary tumor or metastases and recovered Other: No prior investigational anticancer drug No other concurrent investigational agents