PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior biologic or immunologic therapy No prior biologic or immunologic therapy for metastatic disease No concurrent immunotherapy No colony stimulating factors administered concurrently with first course of study therapy, or within 24 hours prior to subsequent courses Chemotherapy: See Disease Characteristics No prior gemcitabine No prior chemotherapy for metastatic disease At least 6 months since prior chemotherapy used as radiosensitization either in the adjuvant setting or for locally advanced disease No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics No prior radiotherapy to more than 25% of bone marrow No concurrent radiotherapy Surgery: See Disease Characteristics