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.