PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy for locoregionally recurrent or metastatic colorectal cancer No concurrent prophylactic growth factor Chemotherapy: No prior chemotherapy for locoregionally recurrent or metastatic colorectal cancer At least 6 months since adjuvant chemotherapy Endocrine therapy: No prior hormone therapy for locoregionally recurrent or metastatic colorectal cancer No concurrent corticosteroids Radiotherapy: See Disease Characteristics No prior radiotherapy for locoregionally recurrent or metastatic colorectal cancer Concurrent localized analgesic radiotherapy of a bone lesion permitted unless indicative of disease progression Surgery: No prior surgery for locoregionally recurrent or metastatic colorectal cancer Other: No other concurrent investigational drug