PRIOR CONCURRENT THERAPY: Biologic therapy: No prior biologic therapy No concurrent biologic therapy Chemotherapy: See Disease Characteristics At least 21 days since prior chemotherapy and recovered No prior systemic treatment with fluorouracil, fluorouracil-uracil, raltitrexed, or capecitabine in combination with gemcitabine Prior fluorouracil or gemcitabine allowed as radiosensitizing agents when given 2 weeks before, during, or 2 weeks after radiotherapy No prior cumulative mitomycin dose greater than 25 mg/m2 Endocrine therapy: Not specified Radiotherapy: At least 21 days since prior radiotherapy and recovered Surgery: No prior surgery No concurrent surgery Other: At least 21 days since prior participation in other investigational study