PRIOR CONCURRENT THERAPY: Biologic therapy: Prior biologic therapy allowed No concurrent immunotherapy Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for mitomycin or nitrosoureas) and recovered No greater than 300 mg/m2 cumulative dose of doxorubicin No concurrent chemotherapy Endocrine therapy: At least 4 weeks since prior hormone therapy No concurrent anticancer hormone therapy Concurrent corticosteroids allowed Radiotherapy: At least 4 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: At least 4 weeks since prior investigational drug therapy No other concurrent investigational therapy