PRIOR CONCURRENT THERAPY: Biologic therapy: No prior immunotherapy No concurrent immunotherapy Chemotherapy: At least 4 weeks since prior gemcitabine therapy and recovered No other prior chemotherapy (except fluorouracil as a radiation enhancing agent) No other concurrent chemotherapy Endocrine therapy: No prior hormonal therapy No concurrent hormonal therapy (except contraceptives, hormone replacement, or megestrol acetate) Radiotherapy: At least 4 weeks since prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: At least 4 weeks since prior investigational agents