Monoclonal Antibody Plus Chemotherapy in Treating Patients With Advanced Colorectal Cancer That Overexpresses HER2

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