PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent biologic therapy Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics At least 4 weeks since prior radiotherapy No concurrent radiotherapy Surgery: See Disease Characteristics At least 4 weeks since prior surgery No concurrent surgery Other: At least 4 weeks since other prior investigational drugs No other concurrent investigational drugs and for 4 weeks after study treatment