Adjuvant Palliative Capecitabine and Gemcitabine in Treating Patients With Locally Advanced or Metastatic Biliary Tract Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed biliary tract cancer * Locally advanced, unresectable, or metastatic disease * Metastatic adenocarcinoma with clinical documentation of gallbladder or bile tree involvement with no evidence of another primary adenocarcinoma allowed * Measurable or nonmeasurable disease * Treatable biliary duct obstruction must be relieved by either internal endoscopic drainage/stenting or palliative bypass surgery before study entry * Symptomatic biliary tract cancer and has at least 1 of the following: * Karnofsky 60-80% * Baseline analgesic consumption at least 10 mg of morphine equivalents per day * Baseline pain intensity score of at least 20 mm out of a possible 100 mm * No prior or concurrent CNS metastasis PATIENT CHARACTERISTICS: Age * 18 to 80 Performance status * See Disease Characteristics * Karnofsky 60-100% Life expectancy * Not specified Hematopoietic * Neutrophil count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 10.0 g/dL Hepatic * Bilirubin no greater than 4 times upper limit of normal (ULN) * Alkaline phosphatase no greater than 5 times ULN * AST and ALT no greater than 5 times ULN Renal * Creatinine clearance greater than 50 mL/min Cardiovascular * No uncontrolled cardiovascular disease Gastrointestinal * Able to ingest oral medication * No malabsorption syndrome * No intractable nausea and/or vomiting * No partial small bowel obstruction Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 1 year after study participation * No active autoimmune disease * No uncontrolled diabetes * No known hypersensitivity to fluorouracil * No known dihydropyrimidine dehydrogenase deficiency * No definitive contraindication to corticosteroids * No prior significant neurologic or psychiatric disorders (e.g., psychotic disorders, dementia, or seizures) that would preclude understanding or providing informed consent * No prior severe reaction to fluoropyrimidine therapy * No psychiatric disorder, cognitive dysfunction, or language problem that would preclude filling out the quality of life questionnaire or patient diary * No other serious underlying medical condition that would preclude study participation * No other malignancy within the past 5 years except nonmelanoma skin cancer or adequately treated carcinoma in situ of the cervix PRIOR CONCURRENT THERAPY: Biologic therapy * No prior biologic therapy * No prior immunotherapy Chemotherapy * No prior chemotherapy for advanced/metastatic disease * No prior palliative chemotherapy Endocrine therapy * No concurrent megestrol Radiotherapy * More than 4 weeks since prior radiotherapy * No concurrent radiotherapy * Treatment of a single painful lesion allowed Surgery * See Disease Characteristics * Prior Whipple procedure allowed * Prior duodenal bypass allowed * No concurrent endoscopic or external biliary drainage as a consequence of progressive malignant bile duct obstruction * Drainage as a consequence of nonmalignant bile duct obstruction allowed Other * More than 30 days since prior treatment within a clinical study * No other concurrent anticancer drugs * No other concurrent investigational drugs * No concurrent sorivudine or its chemically-related analogues (e.g., lamivudine)