To select a better agent between S-1 or gemcitabine in combination with cisplatin for the conventional chemotherapy platform for future development in advanced Biliary Tract Adenocarcinoma (BTA), the investigators conduct a randomized phase II trial of S-1 and cisplatin (SP) versus gemcitabine and cisplatin (GP) as first line therapy in advanced BTA.

Inclusion Criteria:

1. Pathologically proven biliary adenocarinoma
2. Age > 18
3. Evaluable disease
4. ECOG performance status of 2 or better
5. No prior exposure to chemotherapy, but adjuvant chemotherapy (or chemoradiotherapy) completed 6 moths or more before study enrollment is allowed
6. Adequate bone marrow function A. WBCs > 4,000/µL, absolute neutrophil count [ANC]>1,500/µL B. Hemoglobin >9.0 g/dL C. Platelets > 100,000/µL
7. Adequate kidney function (creatinine<1.5 mg/dL)
8. Adequate liver function (bilirubin<1.5 mg/dL [< 2.5 mg/dL for obstructive jaundice with adequately decompressed bile duct obstruction], transaminases levels<3 times the upper normal limit, and serum albumin of >2.5 mg/dL)
9. No serious medical or psychological condition that would preclude study treatment
10. Willingness and ability to comply with scheduled visits, treatment plans, laboratory tests, and other study procedures

Exclusion Criteria:

1. Other tumor type than adenocarcinoma
2. Evidence of GI bleeding or GI obstruction
3. Presence or history of CNS metastasis
4. Pregnancy or breastfeeding
5. Other serious illness or medical conditions
6. Axial skeletal radiotherapy within 6 months
7. Neuropathy grade 2 or worse