This study is a prospective, randomized, single-center randomized controlled clinical trial to investigate the safety and efficacy of ondansetron in reducing the toxicity associated with immune checkpoint inhibitor treatment. This study plans to enroll 134 patients with hepatocellular carcinoma who are scheduled to receive standard ICI treatment. This study will adopt the 2023 CSCO Guidelines for the Management of Immune checkpoint inhibitor-related toxicity as the main assessment criterion, and take the incidence and severity of irAEs as the main observation indicators to evaluate the effectiveness of ondansetron in reducing the toxicity related to immune checkpoint inhibitor treatment in patients with hepatocellular carcinoma.

Inclusion Criteria:

1. Age: 18 to 80 years old, both male and female are acceptable.

2. The imaging or pathological diagnosis is hepatocellular carcinoma;

3. It is planned to carry out standard treatment for liver cancer, specifically including lenvatinib + tislelizumab or lenvatinib + pembrolizumab or atezolizumab + bevacizumab.

4. ECOG score: 0 to 2 points;

5. Expected survival period ≥12 weeks;

6. Baseline blood cell count tests and blood biochemistry must meet the following standards:

   White blood cell count ≥3.0×10^9/L; Hemoglobin ≥90 g/L; The absolute neutrophil count is ≥1.5×10^9/L; Platelet count ≥100×10^9/L; Alanine aminotransferase (ALT), aspartate aminotransferase (AST) ≤ 2.5 times the upper limit of normal (ULN). Total bilirubin ≤ twice ULN; Serum creatinine ≤ 1.5 times ULN; Albumin ≥30 g/L;

7. The subjects voluntarily joined this study, signed the informed consent form, had good compliance and cooperated with the follow-up.

Exclusion Criteria:

1. Those who have received treatment with ondansetron within 14 days;
2. Patients with autoimmune diseases;
3. Use of systemic glucocorticoids or other immunosuppressants within 14 days;
4. Those who have previously discontinued ICI treatment due to irAEs;
5. Those with severe liver dysfunction (Child-Pugh grade C);
6. Those with contraindications to ondansetron such as serotonin syndrome or phenylketonuria;
7. Patients allergic to ondansetron;
8. Those who are currently using drugs that may have serious interactions with ondansetron, such as apopmorphine;
9. The researcher evaluated that the patient was unable or unwilling to comply with the requirements of the research protocol.