PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 6 weeks since chemotherapy No more than 1 prior chemotherapy regimen No prior camptothecin derivatives Endocrine therapy: At least 2 weeks on stable steroid therapy, if necessary Radiotherapy: At least 2 months since prior radiotherapy No prior radiation therapy for recurrent disease Surgery: At least 6 weeks since prior surgery (except biopsy only) Prior surgery for recurrent disease allowed (including stereotactic biopsy or partial resection) Other: No concurrent experimental drugs or anticancer therapy