The aim of this study is to assess the efficacy and safety of durvalumab combined with S-1 as adjuvant therapy of resectable Biliary Tract Cancer(BTC) with high risk of recurrence

Radical surgical resection is still the most important radical treatment for biliary tract tumors, and the postoperative recurrence rate of BTC patients remains high. It is particularly important to choose appropriate and effective adjuvant treatment.

This study is a single center, single arm, prospective, phase II clinical study. This study plans to include 40 BTC patients after radical resection. The patients are evaluated by a multidisciplinary team (MDT) as high risk of recurrence. Adjuvant therapy with durvalumab combined with S-1 should be started no more than 12 weeks after radical surgery. These patients will first receive 8 cycles of adjuvant therapy and the regimens consist of durvalumab and S-1, with a 21-day dosing cycle. After 8 cycles of adjuvant therapy, if the patients do not experience disease recurrence or intolerance，then the patients wil receive 6 cycles of adjuvant therapy in maintenance therapy stage. The regimen of andjuvant therapy is durvalumab with 28-day dosing cycle.

If the patients experience recurrence, the subsequent treatment plan will be determined by the researchers based on treatment guidelines.

Inclusion Criteria:

1. Age ≥ 18 years, both males and females are eligible.
2. Intrahepatic cholangiocarcinoma, extrahepatic cholangiocarcinoma, and gallbladder cancer(Histologically confirmed).
3. TNM stage before surgery: GBC/DCC T2-T4, N+, M0; ICC T1b-T4, N+, M0; PCC, any T, any N, M0 (according to UICC/AJCC TNM staging (8th edition)) .
4. Patients must undergo radical resection, including liver resection or pancreatectomy, before enrollment.
5. Time between surgery and enrollment < 12 weeks.
6. R0 resection.
7. ECOG PS 0-1.
8. No distant metastasis confirmed by MRI.
9. Adequate organ and marrow function, as defined below. Haemoglobin ≥ 9 g/dL Absolute neutrophil count ≥ 1.5 × 109/L Platelet count ≥ 100 × 109/L Serum bilirubin ≤ 1.0 × ULN ALT and AST ≤ 2.5 × ULN Calculated creatinine clearance > 50 mL/minute as determined by Cockcroft-Gault (using actual body weight) or 24-hour urine creatinine clearance.

Exclusion Criteria:

1. Patient diagnosed with Ampulla of Vater(AoV).
2. Time between surgery and enrollment >12 weeks.
3. Receive anti-tumor treatment before surgery, including chemotherapy, radiotherapy, targeted therapy, immunotherapy, local therapy, etc.
4. The tumor was not completely removed, or the postoperative pathology indicated that it was not a biliary tract tumor.
5. Receive other anti-tumor treatments, such as chemotherapy, radiotherapy, or other research drugs, during postoperative adjuvant therapy.
6. Severe infection within 4 weeks before enrollment.
7. Participated in another interventional clinical study.
8. Other factors deemed by the investigator to make the participant unsuitable for participation in this study.