PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior immunotherapy No concurrent colony stimulating factors (e.g., filgrastim (G-CSF) or sargramostim (GM-CSF)) Chemotherapy: No prior topoisomerase I inhibitors (e.g., nitrocamptothecin, aminocamptothecin, irinotecan, or topotecan) At least 4 weeks since prior chemotherapy (at least 6 weeks since prior nitrosoureas, mitomycin, or carboplatin) No other concurrent chemotherapy Endocrine therapy: See Disease Characteristics At least 4 weeks since prior hormonal therapy No concurrent hormonal anticancer therapy Radiotherapy: At least 4 weeks since prior radiotherapy involving at least 30% of the bone marrow No concurrent radiotherapy Surgery: Not specified Other: No other concurrent experimental anticancer medication