PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics No prior irinotecan At least 7 days since other prior chemotherapy and recovered Endocrine therapy: See Disease Characteristics Radiotherapy: See Disease Characteristics Surgery: No ostomy Other: Greater than 1 month since prior investigational agent No concurrent investigational agent No concurrent phenytoin, phenobarbital, valproic acid, or other antiepileptic therapy