PRIOR CONCURRENT THERAPY: Biologic therapy: No prior or concurrent immunotherapy, biologic response modifiers, cytokines, monoclonal antibodies, antitumor vaccines, or any other systemic therapy Chemotherapy: No prior or concurrent chemotherapy Endocrine therapy: No prior or concurrent hormone therapy Hormone replacement after adrenalectomy is allowed Radiotherapy: Prior radiotherapy allowed No concurrent radiotherapy Surgery: Prior nephrectomy allowed Other: No other concurrent investigational drugs No concurrent anticonvulsant therapy