PRIOR CONCURRENT THERAPY: Biologic therapy: At least 3 weeks since prior immunotherapy and recovered No filgrastim (G-CSF) concurrent with nitrocamptothecin Concurrent epoetin alfa allowed Chemotherapy: Prior fluorouracil as radiosensitizer allowed No other prior chemotherapy (e.g., nitrocamptothecin or gemcitabine) No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal or corticosteroid therapy Patients requiring hormonal therapy or corticosteroid therapy for medical reasons may remain on study, but will not be evaluable for clinical benefit response Radiotherapy: At least 3 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: See Disease Characteristics More than 2 weeks since prior major surgery and recovered Prior stent placement allowed No planned surgery within 8 weeks after initiation of treatment