PRIOR CONCURRENT THERAPY: At least 2 weeks since prior cytotoxic therapy (except hydroxyurea and steroids) Biologic therapy: No prior bone marrow transplantation At least 3 days since prior hematopoietic growth factors Chemotherapy: No prior topotecan or camptothecin analogues Prior etoposide allowed Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: Not specified