PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics At least 4 weeks since prior immunotherapy and recovered No concurrent biological response modifier therapy or immunotherapy No concurrent prophylactic growth factors Chemotherapy: See Disease Characteristics No prior camptothecins (e.g., irinotecan or topotecan) At least 4 weeks since other prior chemotherapy (6 weeks for nitrosoureas and mitomycin) and recovered No other concurrent chemotherapy Endocrine therapy: At least 4 weeks since prior hormonal therapy and recovered No concurrent corticosteroids used as anticancer therapy No other concurrent hormonal therapy Radiotherapy: No prior radiotherapy to greater than 25% of bone marrow At least 4 weeks since other prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: No concurrent investigational drug or participation in other clinical study