Capecitabine as Second-Line Therapy in Treating Patients With Stage IV Pancreatic Cancer Who Have the Thymidylate Synthase Gene

DISEASE CHARACTERISTICS: * Histologically confirmed pancreatic cancer * Stage IV disease * Measurable disease (≥ 1 cm or \> 10 mm lesion(s) by spiral CT scan) * Disease progression after ≥ 1 gemcitabine-based treatment regimen for advanced/metastatic disease * Patient carries the double tandem repeat (S/S) variant of the thymidylate synthase gene enhancer region (TSER) * No active CNS metastases (indicated by clinical symptoms, cerebral edema, steroid requirement, or progressive growth) PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * AST/ALT ≤ 2.5 times upper limit of normal (ULN) (5 times ULN if attributable to liver metastases) * Total bilirubin ≤ 1.5 times ULN * Creatinine normal OR creatinine clearance \> 50 mL/min * Fertile patients must use effective contraception during and for 30 days after completion of study treatment * Not pregnant or nursing * Negative pregnancy test * Asymptomatic HIV infection allowed * No recent or ongoing clinically significant gastrointestinal disorder (e.g., malabsorption, bleeding, inflammation, emesis, or diarrhea \> grade 1) * Able to swallow capecitabine tablets * No known hypersensitivity to fluorouracil * No dihydropyrimidine dehydrogenase (DPD) deficiency * No clinically significant cardiac disease (e.g., congestive heart failure, symptomatic coronary artery disease, or cardiac arrhythmias not well controlled with medication) * No myocardial infarction within the past 6 months * No serious, uncontrolled, concurrent infection(s) * No prior unanticipated severe reaction to fluoropyrimidine therapy * No other malignancy within the past 5 years except cured nonmelanoma skin cancer or treated carcinoma in situ of the cervix PRIOR CONCURRENT THERAPY: * See Disease Characteristics * At least 3 weeks since prior chemotherapy * No prior capecitabine except in the adjuvant setting * At least 3 weeks since prior radiotherapy or major surgery * At least 4 weeks since prior participation in any investigational drug study * At least 4 weeks since prior sorivudine or brivudine * No concurrent sorivudine or brivudine * No concurrent cimetidine or azidothymidine (AZT) * Concurrent radiotherapy for bone pain allowed to a limited field provided ≥ 1 indicator lesion remains outside of the field * No other concurrent chemotherapy or immunotherapy