PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior chemotherapy Endocrine therapy: At least 4 weeks since prior hormonal therapy Radiotherapy: At least 4 weeks since prior radiotherapy At least 6 weeks since prior isotope therapy No prior radiotherapy to greater than 30% of bone marrow Surgery: Not specified Other: At least 4 weeks since prior investigational drugs