Exploring the Efficacy and Safety of Tislelizumab in Combination With S-1 in the Treatment of Patients With Postoperative Recurrent High-risk Intrahepatic Cholangiocarcinoma

Inclusion Criteria:

* 18-75 years old, male and female;
* Intrahepatic cholangiocarcinoma was pathologically confirmed after R0 or R1 resection. Patients were also pathologically confirmed to have one of the following high-risk factors (i.e., positive margins, multiple tumor nodes, positive lymph nodes, positive perineural infiltration, intrahepatic cholangiocarcinoma \>5 cm in diameter, and combined vascular invasion);
* Enhanced computed tomography (CT) scans of the chest, abdomen, and pelvis were required within 30 days prior to surgery to demonstrate the absence of distant tumor metastases;
* No history of any chemotherapy, radiotherapy, immunotherapy or interventional therapy within 3 months prior to surgical resection;
* Child-Pugh grade A or B, ECOG score 0-1;
* Normal organ function prior to drug administration: ANC ≥1.5×10\^9/L, Hemoglobin ≥90g/L, PLT \>50\*10\^9/L, serum creatinine (SCr) ≤ 1.5 times the upper limit of normal (ULN) or creatinine clearance ≥50 ml/min (Cockcroft-Gault formula); total bilirubin (TBIL) ≤2 times the upper limit of normal (ULN); glutamine transaminase (AST) or glutamine transaminase (ALT) levels ≤3 times the ULN; urinary protein \<2+ (if urinary protein) upper limit of normal (ULN); albumin transaminase (AST) or alanine transaminase (ALT) levels ≤3 times upper limit of normal (ULN); urine protein \<2+ (if urine protein ≥2+, 24-hour urine protein quantification must show ≤1g of protein); and adequate surgical biliary drainage with no signs of infection.
* Normal coagulation function: a. International normalized ratio INR ≤ 1.5 x ULN; b. Partial thromboplastin time APTT ≤ 1.5 x ULN; c. Prothrombin time PT ≤ 1.5 ULN;
* In case of hepatitis B virus (HBV) infection: if HBsAg-positive, HBV-DNA testing is required and HBV-DNA must be \<2000 IU/mL and willing to receive antiviral therapy throughout the study period; hepatitis C virus (HCV)-RNA-positive patients must have HCV-RNA \<1×10\^3copy/mL and must receive antiviral therapy according to treatment guidelines.
* No major abnormalities in heart, lung or kidney function;
* No history of gastrointestinal hemorrhage;
* Sign the informed consent form.

Exclusion Criteria:

* The tumor is not completely resected, or the pathological diagnosis suggests non-intrahepatic cholangiocarcinoma such as hepatocellular carcinoma, mixed hepatocellular carcinoma, and hepatoportal cholangiocarcinoma;
* Pregnant or breastfeeding women;
* Combined with other malignant tumors;
* Have any active autoimmune disease or a history of autoimmune disease;
* Uncontrolled clinically significant cardiac disease, including but not limited to the following: (1) \> NYHA II congestive heart failure; (2) unstable angina pectoris; (3) myocardial infarction within the last 1 year; (4) clinically significant supraventricular arrhythmia or ventricular arrhythmia requiring treatment or intervention;
* The patient has a congenital or acquired immunodeficiency;
* Uncontrollable infection \> grade 2 (NCI-CTC version 5.0);
* Psychopaths;
* Patients have participated in other clinical trials within the past three months;
* Postoperative patients receiving other targeted agents, immunotherapy such as PD-1 antibodies, and FOLFOX systemic chemotherapy;
* Patients who are not suitable to participate in the study as determined by the investigator.