PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No more than 1 prior adjuvant chemotherapy regimen and 1 for recurrence (Gliadel is considered 1 regimen) At least 4 weeks since prior chemotherapy At least 6 weeks since prior nitrosoureas No prior irinotecan, topotecan, or aminocamptothecin Endocrine therapy: At least 2 weeks on fixed dose of corticosteroids (or no corticosteroids) prior to baseline scan Radiotherapy: At least 8 weeks since prior radiotherapy Surgery: No surgical resection between last radiotherapy or chemotherapy and study therapy, unless unequivocal tumor growth since surgery