DISEASE CHARACTERISTICS: Histologically, cytologically, and/or radiographically proven metastatic colorectal cancer with disease recurrence or progression following fluorouracil (5-FU) based chemotherapy Acceptable 5-FU based regimens include capecitabine, 5-FU-uracil, floxuridine, S-1, or eniluracil combined with 5-FU Acceptable 5-FU modulating agents include levamisole and leucovorin calcium Measurable or evaluable disease No known brain or leptomeningeal disease except previously irradiated lesions that do not require corticosteroids and are asymptomatic