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