DISEASE CHARACTERISTICS: Histologically or cytologically confirmed metastatic adenocarcinoma of the colon or rectum that is not amenable to potentially curative therapy (e.g., inoperable metastatic disease) At least 1 unidimensionally measurable lesion at least 20 mm in diameter by conventional CT or MRI scan or at least 10 mm in diameter by spiral CT scan Progressive disease by CT or MRI scan during or no more than 6 months after the last dose of prior first-line irinotecan, fluorouracil, and leucovorin calcium (Saltz regimen) for metastatic disease