Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed stage IV colorectal cancer with p185 HER2 overexpression

- Bidimensionally measurable disease Indicator lesion must be outside of irradiated
field No symptomatic CNS brain metastases

PATIENT CHARACTERISTICS:

- Performance status: ECOG 0-2

- Absolute granulocyte count at least 1,500/mm3

- Platelet count at least 100,000/mm3

- Bilirubin no greater than 1.5 times upper limit of normal (ULN)

- SGOT no greater than 3.0 times ULN

- Creatinine no greater than 2.0 mg/dL

- LVEF at least 45% by MUGA or ECHO

- No myocardial infarction within the past 6 months

- No congestive heart failure

- No unstable angina

- No clinically significant pericardial effusion or arrhythmia

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception during and for 6 months after study

- No other prior malignancy within the past 5 years, except:

- Curatively treated basal or squamous cell skin cancer

- Curatively treated carcinoma in situ of the cervix

- No active serious infection or serious underlying medical condition that would
prevent compliance

- No dementia or significantly altered mental status

PRIOR CONCURRENT THERAPY:

- Concurrent filgrastim (G-CSF), sargramostim (GM-CSF), or epoetin alfa allowed

- No prior trastuzumab

- No more than 1 prior chemotherapy regimen for advanced disease (if progressed during
or within 6 months of adjuvant therapy considered to have had 1 regimen for advanced
disease)

- No prior irinotecan

- Concurrent contraception, estrogen replacement therapy, or megestrol acetate for
anorexia allowed

- Greater than 3 weeks since prior radiotherapy and recovered

- Greater than 3 weeks since major surgery (except simple biopsy or venous access
placement) and recovered

- At least 3 weeks since prior investigational nonneoplastic drugs