Inclusion Criteria

DISEASE CHARACTERISTICS: Histologically or cytologically proven colorectal cancer with
failure or relapse after at least 1 prior fluorouracil based chemotherapy regimen for
advanced disease OR metastatic disease within 6 months after completion of adjuvant
therapy No more than 1 prior fluorouracil based chemotherapy regimen for metastatic
disease Prior oral fluorouracil or combinations of other drugs with fluorouracil allowed
Prior adjuvant therapy with fluorouracil allowed and not counted as 1 regimen if given
more than 1 year prior to study At least 1 bidimensionally measurable indicator lesion
that has not been irradiated and has the following minimum dimensions: Skin nodule or
superficial lymph node: 2 x 2 cm Lung lesion surrounded by aerated lung: 1 x 1 cm by chest
x-ray or at least 2 cm in 1 dimension by CT scan Liver lesion, soft tissue mass, or lymph
node: at least 2 cm in 1 dimension by CT scan or sonogram

PATIENT CHARACTERISTICS: Age: Not specified Performance status: ECOG 0-2 Life expectancy:
At least 8 weeks Hematopoietic: Granulocyte count greater than 1,500/mm3 Hemoglobin
greater than 10 g/dL Platelet count greater than 100,000/mm3 Hepatic: SGOT and SGPT no
greater than 3 times normal (no greater than 5 times normal if liver tumor present)
Bilirubin no greater than 2 mg/dL Renal: Creatinine no greater than 2 mg/dL Other: Not
pregnant or nursing Negative pregnancy test Fertile patients must use effective
contraception during and for 6 months after study

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 2 weeks since prior immunotherapy and
recovered No concurrent filgrastim (G-CSF) No concurrent immunotherapy Chemotherapy: See
Disease Characteristics No prior nitrocamptothecin, irinotecan, or other camptothecin
analog At least 2 weeks since other prior chemotherapy and recovered No other concurrent
chemotherapy Endocrine therapy: No concurrent anticancer hormonal therapy Radiotherapy:
See Disease Characteristics At least 2 weeks since prior radiotherapy and recovered No
concurrent radiotherapy Surgery: At least 2 weeks since prior surgery and recovered No
scheduled major surgery within 8 weeks following initiation of treatment