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Simple Summary: Surrogate radiology-based endpoints such as progression-free survival (PFS) and objective response rate (ORR) are commonly used in oncology. However, their surrogacy with overall survival (OS) has not been evaluated in immunotherapy trials for hepatocellular carcinoma (HCC). We found that the surrogacy of PFS with OS is highly variable depending on treatment class (immune-checkpoint inhibitors or multikinase inhibitors) and evaluation time-point. Early PFS is a robust surrogate endpoint for OS in immunotherapy trials, while the surrogacy relationship between ORR and OS is weak. Early assessment of PFS could be useful for allowing analyses with small sample sizes and short accrual times, enhancing the interpretability of immunotherapy trials in HCC. Background: Radiology-based outcomes, such as progression-free survival (PFS) and objective response rate (ORR), are used as surrogate endpoints in oncology trials. We aimed to assess the surrogacy relationship of PFS with overall survival (OS) in clinical trials of systemic therapies targeting advanced hepatocellular carcinoma (HCC) by novel meta-regression methods. Methods: A search of databases (PubMed, American Society of Clinical Oncology (ASCO), and European Society for Medical Oncology (ESMO) Meeting Libraries, Clinicaltrials.gov) for trials of systemic therapies for advanced HCC reporting both OS and PFS was performed. Individual patient data were extracted from PFS and OS Kaplan–Meier curves. Summary median PFS and OS data were obtained from random-effect model. The surrogate relationships of median PFS, first quartile (Q1), third quartile (Q3), and restricted mean survival time (RMST) for OS were evaluated by the coefficient of determination R2. Heterogeneity was explored by meta-regression. Results: We identified 49 trials, 11 assessing immune-checkpoint inhibitors (ICIs) and 38 multikinase inhibitors (MKIs). Overall, the correlation between median PFS and median OS was weak (R2 = 0.20. 95% Confidence Intervals [CI]-0.02;0.42). Surrogacy robustness varied between treatment classes and PFS endpoints. In ICI trials only, the correlations between Q1-PFS and Q1-OS and between 12-month PFS-RMST and 12-month OS-RMST were high (R2 = 0.89, 95%CI 0.78–0.98, and 0.80, 95% CI 0.63–0.96, respectively). Interaction p-values obtained by meta-regression confirmed the robustness of results. Conclusions: In trials of systemic therapies for advanced HCC, the surrogate relationship of PFS with OS is highly variable depending on treatment class (ICI or MKI) and evaluation time-point. In ICI trials, Q1-PFS and 12-month PFS-RMST are robust surrogate endpoints for OS. [ABSTRACT FROM AUTHOR]