Inclusion Criteria

DISEASE CHARACTERISTICS:

- Diagnosis of metastatic colorectal adenocarcinoma incurable by surgery or not
amenable to radiotherapy with curative intent

- Progressive disease no more than 3 months after completion of a prior weekly
irinotecan, fluorouracil, and leucovorin calcium chemotherapy regimen

- At least 1 measurable lesion At least 20 mm in at least one dimension

- No known CNS metastases or carcinomatous meningitis

PATIENT CHARACTERISTICS:

- Age: 18 and over

- Performance status: ECOG 0-2

- Life expectancy: At least 12 weeks

- Absolute neutrophil count greater than 2,000/mm3

- Platelet count at least 100,000/mm3

- Bilirubin no greater than 0.5 mg/dL above upper limit of normal (ULN)

- AST no greater than 5 times ULN

- Creatinine no greater than 1.5 times ULN OR creatinine clearance greater than 60
mL/min

- No unstable angina No symptomatic congestive heart failure

- No serious uncontrolled cardiac arrhythmia

- No active or uncontrolled infection

- No evidence of other serious illness

- No other malignancy within the past 5 years except adequately treated basal cell or
squamous cell skin cancer or noninvasive carcinomas

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

- No concurrent sargramostim (GM-CSF)

- At least 4 weeks since prior chemotherapy

- No more than 1 prior chemotherapy regimen for advanced colorectal cancer

- Prior adjuvant chemotherapy allowed

- No prior radiotherapy to more than 25% of bone marrow

- At least 4 weeks since prior major surgery