• Death from colorectal cancer [ Designated as safety issue: No ]
• Disease recurrence [ Designated as safety issue: No ]

• Death from colorectal cancer
• Disease recurrence

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.

OBJECTIVES:

• Compare all-cause mortality in patients with resected colorectal cancer treated with adjuvant chemotherapy with L-leucovorin and fluorouracil vs observation.
• Compare the recurrence rates in patients treated with this regimen vs observation.
• Compare the effectiveness of a monthly 5-day schedule vs a once weekly schedule of L-leucovorin and fluorouracil in this patient population.

OUTLINE: This is a randomized, open-label, multicenter study. Patients are randomized to receive adjuvant chemotherapy (arm I) or undergo observation only (arm II).

• Arm I: Within 12 weeks of surgery, patients receive L-leucovorin IV followed by fluorouracil IV on days 1-5 every 4 weeks for 6 courses. Alternatively, patients may receive L-leucovorin IV followed by fluorouracil IV on day 1 weekly for 30 weeks.
• Arm II: Patients undergo observation. Patients are followed annually.

PROJECTED ACCRUAL: A total of 2,500 patients (1,250 per arm) will be accrued for this study.

• Drug: L-leucovorin
• Drug: fluorouracil
• Procedure: adjuvant therapy

DISEASE CHARACTERISTICS:

• Completely resected stage II or III colorectal cancer
• No distant metastases
• No positive resection margins
• No positive peritoneal washings

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• Not specified

Life expectancy:

• Not specified

Hematopoietic:

• Not specified

Hepatic:

• Not specified

Renal:

• Not specified

Other:

• No clear definite indication for, or contraindication against, systemic chemotherapy with L-leucovorin and fluorouracil

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• No concurrent chemotherapy in observation only arm

Endocrine therapy:

• Not specified

Radiotherapy:

• Concurrent radiotherapy allowed in adjuvant chemotherapy arm provided chemotherapy administered on the once weekly schedule

Surgery:

• See Disease Characteristics