A Trial to Evaluate the Safety and Efficacy of the Combination of the Oncolytic Immunotherapy Pexa-Vec With the PD-1 Receptor Blocking Antibody Nivolumab in the First-line Treatment of Advanced Hepatocellular Carcinoma (HCC)

Inclusion Criteria: * Histological/cytological diagnosis of primary HCC, excluding cholangiocarcinoma, hepatocholangiocarcinoma, fibrolamellar carcinoma and hepatoblastoma * Advanced stage HCC per EASL-EORTC (European Association for the Study of the Liver-European Organisation for Research and Treatment of Cancer) guidelines, i.e. patients who are not candidates for curative interventions and not candidates for locoregional modalities * Patients naïve to systemic therapy for HCC * Tumor status (as determined by radiology evaluation): At least one measurable viable tumor in the liver, ≥1 cm longest diameter (LD), using a dynamic imaging technique (arterial phase of triphasic computerized tomography \[CT\] scan, or dynamic contrast-enhanced magnetic resonance imaging \[MRI\]), and injectable under imaging-guidance (CT or ultrasound) * At least one tumor that has not received prior local-regional treatment, or that has exhibited definitive growth of viable tumor since prior local-regional treatment of HCC undertaken at least 4 weeks prior to enrolment or 3 months prior to enrolment for radioembolization * Child-Pugh Class A. Note: paracentesis, albumin infusion or diuretic treatment cannot be used to downgrade Child-Pugh score (e.g., to improve from severe to moderate/mild or from moderate to mild ascites) * Performance status 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) scale * Adequate hematological, hepatic, and renal function * Additional inclusion criteria exist Exclusion Criteria: * Histological diagnosis of cholangiocarcinoma, hepatocholangiocarcinoma, fibrolamellar carcinoma and hepatoblastoma * Symptomatic cardiovascular disease, including but not limited to significant coronary artery disease (e.g., requiring angioplasty or stenting) or congestive heart failure within the preceding 12 months * Current or past history of cardiovascular disease (e.g., past history of myocardial infarction, ischemic cardiomyopathy) unless cardiology consultation and clearance has been obtained for study participation * History of moderate or severe ascites, bleeding esophageal varices, hepatic encephalopathy or pleural effusions related to liver insufficiency within 6 months of screening; patients with adequately treated esophageal varices are allowed * Active, known or suspected significant immunodeficiency due to underlying illness including HIV/AIDS, autoimmune diseases, and/or immune-suppressive medication including high-dose corticosteroids * History of severe eczema and/or ongoing severe inflammatory skin condition (as determined by the Investigator) requiring medical treatment * Any known allergy or reaction to any component of nivolumab formulation or its excipients * Additional exclusion criteria exist