PRIOR CONCURRENT THERAPY: Biologic therapy: No prior bone marrow or peripheral blood stem cell transplantation Recovered from prior immunotherapy At least 4 weeks since prior biologic therapy and recovered Concurrent growth factors allowed Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered No prior 506U78 therapy No other concurrent chemotherapy Endocrine therapy: See Disease Characteristics No concurrent corticosteroid therapy greater than 10 mg/day of prednisone equivalent No concurrent corticosteroids as antiemetics Concurrent hormone replacement therapy or oral contraceptives allowed Concurrent hydrocortisone as prophylaxis or treatment of transfusion reactions allowed Radiotherapy: At least 4 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: No other concurrent anticancer agents