PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 8 weeks since nitrosoureas (e.g., CCNU, BCNU, mitomycin) At least 4 weeks since any other chemotherapy Recovered from all toxic effects Endocrine therapy: Not specified Radiotherapy: No prior irradiation of more than 25% of the marrow Surgery: Not specified Other: No concurrent nonsteroidal anti-inflammatory agents or aspirin