PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics No concurrent immunotherapy including filgrastim (G-CSF) Chemotherapy: See Disease Characteristics No prior topoisomerase I inhibitors (e.g., irinotecan, topotecan, or aminocamptothecin) At least 4 weeks since other prior chemotherapy and recovered No other concurrent chemotherapy Endocrine therapy: No concurrent anticancer hormonal therapy Radiotherapy: No prior radiotherapy to major bone marrow-containing areas (e.g., pelvis, lumbar spine) No prior radiotherapy to sole indicator lesion At least 4 weeks since prior limited radiotherapy and recovered No concurrent radiotherapy Surgery: At least 1 week since prior minor surgery and recovered At least 3 weeks since prior major surgery and recovered Other: No concurrent phenytoin, phenobarbital, or other antiepileptic prophylaxis