e15527 Background: Optimal chemotherapy for unresectable biliary tract cancer is yet to be defined. We have conducted the phase II trial of Gemcitabine (GEM) with S-1, oral fluorouracil prodrug tegafur combined with two modulators, 5-chloro-2, 4-dihydropridine and potassium oxonate to evaluate the activity and toxicity of such combination in patients with unresectable biliary tract cancer. Methods: Eligibility criteria were pathologically-proven biliary tract cancer, appropriate performance status 0 to 2, age 20 to 79 years, adequate hematological, renal and liver functions, no prior chemotherapy, and written informed consent. S-1 was given orally (30mg/m2) bid for 14 consecutive days and GEM (1000mg/m2) was given on day 8 and 15. Cycle was repeated every 21 days. Results: 30 patients with unresectable biliary tract cancer (Gall-bladder: intrahepatic bile ducts: extrahepatic bile ducts=7:16:7) were enrolled from March 2007 to December 2008. Patients characteristics were: median age; 67 (46–79), male/female; 20/10, PS 0/1/2; 16/13/1. Median number of cycles was 8 (range 1 to 14). Out of total 26 evaluable patients, objective responses were observed in 9 patients (30%); 16 patients achieved stable disease and 1 patients showed disease progression. Median survival was 390 days (95% c.i.: 290 - 490 days). The grade 3–4 toxicities observed were leucopenia (20%), neutropenia (40%), anemia (17%), thrombocytopenia (37%), anorexia (7%), fever (10%), rash (7%) and interstitial pneumonia (7%). Conclusions: The combination chemotherapy with GEM and S-1 was well tolerated and high response rate has been observed. This result is very promising but survival benefit against GEM monotherapy should be demonstrated in future phase 3 studies. No significant financial relationships to disclose.