RATIONALE: Drugs used in chemotherapy, such as tegafur-uracil, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Giving chemotherapy after surgery may kill any tumor cells that remain after surgery. Sometimes, after surgery, the tumor may not need more treatment until it progresses. In this case, observation may be sufficient. It is not yet known whether chemotherapy is more effective than observation in treating colorectal cancer.

PURPOSE: This randomized phase III trial is studying tegafur and uracil to see how well they work compared to observation in treating patients with stage II colorectal cancer that has been completely removed by surgery.

OBJECTIVES:

Primary

• Compare the efficacy of adjuvant tegafur-uracil vs observation only in patients with curatively resected stage II colorectal cancer.

Secondary

• Compare relapse-free and overall survival of patients treated with these regimens.
• Compare the occurrence of adverse events in patients treated with these regimens.

OUTLINE: This is a randomized, controlled study. Patients are randomized to 1 of 2 treatment arms.

• Arm I: Patients undergo observation.
• Arm II: Patients receive oral tegafur-uracil on days 1-5. Treatment repeats every 7 days for 1 year in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed periodically for 5 years.

PROJECTED ACCRUAL: A total of 2,000 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the colon or rectosigmoid

  • Stage II disease

• Has undergone curative (R0) resection within the past 8 weeks

• No suspicion of hereditary colorectal cancer

• No severe postoperative complications

PATIENT CHARACTERISTICS:

• ECOG performance status 0-1

• WBC 3,500-12,000/mm³

• Absolute neutrophil count ≥ 1,500/mm³

• Platelet count ≥ 100,000/mm³

• Hemoglobin ≥ 9.0 g/dL

• Bilirubin ≤ 2.0 mg/dL

• AST and ALT ≤ 100 IU/L

• Creatinine ≤ 1.5 mg/dL

• Not pregnant or nursing

• Able to take oral medications

• Major organ functions are preserved

• No other active malignancy

• None of the following conditions:

  • Uncontrolled diabetes mellitus
  • Uncontrolled hypertension
  • Myocardial infarction or unstable angina pectoris within the past 6 months
  • Liver cirrhosis
  • Interstitial pneumonia
  • Pulmonary fibrosis
  • Severe emphysema

• No psychiatric disease or other condition that would preclude study participation

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• No prior chemotherapy
• No prior or concurrent radiotherapy
• No concurrent prophylactic growth factors
• No concurrent biologic response modifiers