PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks since prior nitrosourea, procarbazine, or mitomycin) and recovered Endocrine therapy: Concurrent corticosteroid therapy must be stable for at least 1 week prior to study, if clinically possible Radiotherapy: At least 4 weeks since prior radiotherapy and recovered Surgery: Not specified