The objective of this study is to evaluate the safety of GCS therapy for phase I and efficacy of GCS therapy for phase II.

Biliary tract cancer is one of the most lethal malignancies worldwide, with surgery representing the only potentially curative treatment for this disease. However, many patients are diagnosed too late for curative resection, and even if surgery can be performed, the likelihood of relapse is very high. Over the past decade, gemcitabine has been widely used to treat unresectable or recurrent biliary tract cancer patients. In the ABC-02 study, the first prospective multicenter phase III study in this field, gemcitabine/cisplatin combination chemotherapy was compared with gemcitabine monotherapy and found that the combination regimen significantly prolonged MST (from 8.1 to 11.7 months; P < 0.001). Gemcitabine/cisplatin combination therapy is now considered to be the standard regimen for advanced biliary tract cancer. S-1 is an oral fluoropyrimidine prodrug that has confirmed efficacy against various solid tumors, both alone and in combination with other cytotoxic drugs. S-1 monotherapy has yielded good results against advanced biliary tract cancer and gemcitabine/S-1 combination therapy has yielded promising results with acceptable toxicity levels for patients with advanced biliary tract cancer. In this study, we aimed to determine the safety and efficacy of adding S-1 to gemcitabine/cisplatin combination regimen for advanced biliary tract cancer.

Inclusion Criteria:

• 1. Patients with cytologically or histologically proved biliary tract cancer 2. age >=20 years 3. PS 0-2 4. No prior history of chemotherapy or radiotherapy. Patients who have undergone adjuvant chemotherapy are eligible if at least 6 months have passed since the last administration.

  5. Adequate bone marrow function (neutrophil count >=1,500/mm3, and platelet count >=100,000/mm3), liver function (total bilirubin >=3 mg/dL and AST/ALT >=150 IU/L), and renal function (creatinine clearance >=60 mL/min) 6.No other serious comorbid disease 7.Adequate oral intake 8.Provided written informed consent

Exclusion Criteria:

• 1. Patients with interstitial pneumonia or pulmonary fibrosis 2. Patients with uncontrollable diabetes mellitus, liver disease, angina pectoris or a new onset of myocardial infarction within 3 months 3. Patients with severe active infection 4. Patients who are pregnant or lactating, or have an intention to get pregnant 5. Patients with a history of severe drug allergy 6. Patients with other serious comorbid disease 7. Patients with mental disease 8. Patients who are judged inappropriate for the entry into the study by the principle doctor 9. Patients with watery diarrhea