Biological Therapy With Combination Chemotherapy in Patients With Colorectal Cancer

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.