PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy At least 6 weeks since prior nitrosourea, procarbazine, or mitomycin and recovered No prior nitrosourea greater than 1,200 mg/m2 Endocrine therapy: Concurrent stable dose corticosteroids allowed if on for at least two weeks prior to study Radiotherapy: At least 4 weeks since prior radiotherapy Surgery: Not specified