DISEASE CHARACTERISTICS: Histologically proven metastatic, advanced, or locally recurrent fluorouracil (5-FU) refractory adenocarcinoma of the colon or rectum Progression of disease within 6 months of receiving adjuvant 5-FU based chemotherapy OR Progression of disease during or following completion of 5-FU based chemotherapy for metastatic disease No more than 1 failure with a 5-FU regimen for recurrent, advanced, or metastatic disease Failure on 5-FU adjuvant therapy must accompany failure on 5-FU therapy for metastatic disease Bidimensionally measurable disease CNS metastases allowed only with measurable disease in other sites Prior treatment for CNS metastases required