PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics Chemotherapy: No other concurrent cytotoxic drugs Endocrine therapy: Concurrent steroids allowed but must be tapered to less than 0.5 mg/kg/day of prednisone or equivalent prior to starting study drug (if symptomatic flare develops during taper, patients may continue on the lowest dose thought to produce stabilization) Radiotherapy: Not specified Surgery: Not specified Other: Concurrent cyclosporine and other nonmyelosuppressive drugs allowed No concurrent myelosuppressive agents (azathioprine, mercaptopurine)