RATIONALE: Biological therapies use different ways to stimulate the immune system and stop cancer cells from growing. Combining chemotherapy with biological therapy may kill more tumor cells.

PURPOSE: Randomized phase III trial to compare the effectiveness of treatment using levamisole with treatment using interferon alfa and combination chemotherapy consisting of fluorouracil and leucovorin in patients with stage II or stage III colorectal cancer.

OBJECTIVES:

• Assess the efficacy of the addition of levamisole or alfa interferon to fluorouracil and leucovorin calcium (folinic acid) as an adjuvant treatment of intraperitoneal colorectal cancer.

OUTLINE: This is a three arm study. Patients are randomized to receive either levamisole, alfa interferon, or no treatment.

• Arm I: Patients receive levamisole PO for 3 days every 2 weeks for 6 months before and after surgery. Fluorouracil IV bolus and leucovorin calcium (folinic acid) IV over 1 hour are administered on days 1-5 every 4 weeks for 6 cycles after surgery.
• Arm II: Patients receive alfa interferon-2a SC on 3 alternate days for a week before surgery and for 6 months after surgery. Fluorouracil IV bolus and folinic acid IV over 1 hour are administered on days 1-5 every 4 weeks for 6 cycles after surgery.
• Arm III: Patients undergo surgery followed by fluorouracil IV bolus and folinic acid IV over 1 hour on days 1-5 every 4 weeks for 6 cycles.

Patients are followed every 3 months for 2 years, then every 6 months.

PROJECTED ACCRUAL: 350 patients per arm will be accrued for a total of 1,050 patients.

DISEASE CHARACTERISTICS:

• Histologically confirmed stage T3-T4 N0 or T1-T4 N1-3 colorectal cancer
• No evidence of residual disease after surgery
• Tumor located above peritoneal reflection
• No distant metastases

PATIENT CHARACTERISTICS:

Age:

• 75 and under

Performance status:

• WHO 0-1

Life expectancy:

• Not specified

Hematopoietic:

• WBC at least 3500/mm3
• Platelet count at least 100,000/mm3

Hepatic:

• Bilirubin no greater than 2.0 mg/dL
• SGPT less than 2 times upper limit of normal

Renal:

• Creatinine no greater than 2.0 mg/dL

Cardiovascular:

• No serious cardiac ischemia

Other:

• Adequate metabolic functions
• No prior neoplasm
• No prior/concurrent illness
• No insulin-dependent diabetes

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No prior immunotherapy for the current cancer

Chemotherapy

• No prior chemotherapy for the current cancer

Endocrine therapy

• Not specified

Radiotherapy

• No prior radiotherapy for the current cancer

Surgery

• Not specified