PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics At least 5 days since prior hematopoietic growth factors Chemotherapy: See Disease Characteristics At least 24 hours since prior hydroxyurea At least 2 weeks since other prior cytotoxic anticancer therapy Prior carboplatin, fludarabine, or topotecan allowed Endocrine therapy: Concurrent corticosteroids allowed Radiotherapy: Not specified Surgery: Not specified