Capecitabine or Observation After Surgery in Treating Patients With Biliary Tract Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed biliary tract cancer (including intrahepatic or extrahepatic/hilar cholangiocarcinoma or muscle invasive gallbladder cancer or cancer of the distal bile duct) * Must have undergone a radical surgical approach which includes liver resection, pancreatic resection, or less commonly both * Patients with pathological evidence of microscopic involvement of the margins of the excised specimen are eligible as long as resection is macroscopically complete * Must be able to start treatment within 12 weeks of surgery * No pancreatic or periampullary cancer * No mucosal gallbladder cancer PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Urea \< 1.5 times upper limit of normal (ULN) * Creatinine \< 1.5 times ULN * Glomerular filtration rate ≥ 60 mL/min (if \< 60 mL/min, adequate renal function for capecitabine must be confirmed by isotope EDTA) * Hemoglobin ≥ 10 g/dL * WBC ≥ 3,000/mm³ * Absolute neutrophil count ≥ 1,500/mm³ * Platelet count ≥ 100,000/mm³ * Bilirubin ≤ 3 times ULN * ALT and AST ≤ 5 times ULN * Adequate surgical biliary drainage with no evidence of infection * Not pregnant or nursing * Negative pregnancy test for women of childbearing age and childbearing potential * Fertile patients must use effective contraception during study treatment and for at least 3 months after study treatment has ended * Must provide written informed consent * No history of other malignant diseases within the past 5 years other than adequately treated nonmelanoma skin cancer or in situ carcinoma of the uterine cervix * No serious co-existing medical condition likely to interfere with protocol treatment, including a potential serious infection * No evidence of significant clinical disorder or laboratory finding that makes it undesirable for the patient to participate in the trial * No psychological, familial, sociological, or geographical factors considered likely to preclude study compliance * No other serious uncontrolled medical conditions * No unresolved biliary tree obstruction PRIOR CONCURRENT THERAPY: * See Disease Characteristics * Completely recovered from prior surgery * No use of other investigational agents within 28 days prior to and during study treatment * No prior chemotherapy or radiotherapy for biliary tract cancer * No other concurrent anticancer chemotherapy, radiotherapy, or investigational agent