PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy for metastatic disease No concurrent immunotherapy Chemotherapy: See Disease Characteristics No prior chemotherapy for metastatic disease No prior radiosensitizing chemotherapy in metastatic setting At least 6 months since prior adjuvant therapy No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics At least 4 weeks since prior radiotherapy and recovered No prior radiotherapy to major bone marrow containing areas (e.g., pelvis, lumbar spine) No prior radiotherapy to only evaluable lesion No concurrent radiotherapy Surgery: At least 1 week since minor surgery and 3 weeks since major surgery and recovered Other: No concurrent phenytoin, phenobarbital, or other antiepileptic prophylaxis No concurrent prochlorperazine on day of irinotecan administration No other concurrent medications except for analgesics, chronic treatments for concurrent medical conditions, or agents required for life threatening medical problems