PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior immunotherapy and recovered No prior bone marrow transplantation Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for carboplatin, nitrosoureas, or mitomycin) and recovered Endocrine therapy: At least 1 week since prior hormonal therapy and recovered Concurrent hormone replacement therapy allowed No concurrent chronic steroid therapy Radiotherapy: At least 4 weeks since prior radiotherapy and recovered No prior radiotherapy to study lesions or to more than 30% of bone marrow containing areas Surgery: Not specified Other: At least 4 weeks since other prior investigational drugs No other concurrent investigational drugs Any regimens for other concurrent diseases or medical conditions must be stable for at least 4 weeks