PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 6 weeks since prior chemotherapy No prior irinotecan or carmustine treatment failure No more than 1 prior chemotherapy regimen Endocrine therapy: Patients taking corticosteroids must be on a stable dose for at least 1 week prior to study and the dose should not escalate over entry dose level Radiotherapy: At least 6 weeks since prior radiotherapy Surgery: At least 3 weeks since prior surgical resection Other: No concurrent medication that may interfere with study results