This study is a single-cohort study. Pediatric patients with advanced, relapsed/refractory hepatoblastoma who have previously failed first-line or higher systemic therapy will receive 2 cycles of treatment with sintilimab combined with lenvatinib and chemotherapy (irinotecan). Patients may discontinue treatment due to disease progression, death, intolerable toxicity, withdrawal of informed consent, initiation of new anti-tumor therapy, or other reasons specified in the protocol, whichever occurs first.
* Dose setting: * Sintilimab: The recommended dose is 3 mg/kg (maximum dose not exceeding 200 mg per administration), administered by intravenous infusion (60±15 minutes) once daily on Day 1. * Lenvatinib: 7 mg/m² (maximum 12 mg), taken orally once daily on Days 1-21. * Chemotherapy (irinotecan hydrochloride injection): * Irinotecan hydrochloride injection: 50 mg/m², administered by intravenous infusion once daily on Days 1-5. * Each 3 weeks constitutes one cycle. For patients who discontinue the study drug without radiological progression, follow-up and tumor assessment will continue until progressive disease (PD) occurs, new anti-tumor therapy is initiated, or death. * Tumor tissues and peripheral blood of patients will be collected for relevant tests.
Absolute Neutrophil Count (ANC) ≥1.5×10⁹/L;
Platelet count ≥100×10⁹/L;
Total bilirubin ≤1.5×Upper Limit of Normal (ULN);
Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) ≤2.5×ULN (for participants with liver metastases, ALT or AST ≤5×ULN is allowed);
Positive for human immunodeficiency virus (HIV) (HIV1/2 antibodies);
Active tuberculosis;
Other uncontrolled active infections (CTCAE V5.0 >Grade 2); Failure to recover from surgery, such as unhealed incisions or severe postoperative complications; Vaccination with any live-attenuated vaccine within 4 weeks before enrollment or likely to be administered during the study period; seasonal influenza vaccines without live viruses are allowed.