Heterogeneity of Treatment Effects of Adding Locoregional Therapies to Atezolizumab Plus Bevacizumab in Patients With Unresectable Hepatocellular Carcinoma (ISMIO-026)

Inclusion Criteria: * Age ≥18 years on the index date. * Receipt of at least one dose each of atezolizumab and bevacizumab as part of the same first-line combination regimen, with an interval of ≤28 days between the first administrations of the two drugs. * At least one intrahepatic lesion amenable to a protocol-specified LRT on the index date, with no absolute contraindication to Atezo+Bev or to all feasible LRTs. * A clinical, radiologic, or pathologic diagnosis of uHCC on or before the index date; baseline EHS is permitted. * Survival status or the date last known alive after the index date can be ascertained. * No systemic therapy for HCC before the regimen initiation date. * No LRT within 60 days before the index date or between baseline imaging and the index date; earlier prior LRTs are permitted provided that an untreated, measurable intrahepatic lesion remains. * A technically adequate baseline contrast-enhanced CT/MRI examination and at least one untreated intrahepatic lesion that can be delineated and evaluated. * Baseline ECOG performance status of 0-2. Exclusion Criteria: * Another primary malignancy requiring active systemic treatment on the index date, except for a malignancy that has been cured and has a low risk of recurrence. * Participation on the index date in an interventional study that could affect treatment allocation or outcome assessment. * Suitability for immediate curative resection or liver transplantation following multidisciplinary assessment. * An absolute contraindication to Atezo+Bev or to all feasible LRTs. * Active autoimmune disease or immunodeficiency requiring systemic immunosuppression or constituting a contraindication to atezolizumab. Inadequately controlled high-risk esophageal/gastric varices, recent variceal bleeding, an uncorrected bleeding tendency, or clinically significant coagulopathy. * Inability to determine the index date, primary treatment strategy, OS outcome/censoring date, or absence of a technically adequate baseline contrast-enhanced CT/MRI examination.