Safety and Efficacy of Pembrolizumab (MK-3475) Versus Placebo as Adjuvant Therapy in Participants With Hepatocellular Carcinoma (HCC) and Complete Radiological Response After Surgical Resection or Local Ablation (MK-3475-937 / KEYNOTE-937)

Inclusion Criteria: * Has a diagnosis of HCC by radiological criteria and/or pathological confirmation. * Has an eligibility scan (CT of the chest, triphasic CT scan or MRI of the abdomen, and CT or MRI of the pelvis) confirming complete radiological response ≥4 weeks after complete surgical resection or local ablation. Randomization needs to occur within 12 weeks of the date of surgical resection or local ablation. * Has no radiologic evidence of disease prior to enrollment. * Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 within 7 days prior to Cycle 1, Day 1. * Has a Child-Pugh class A liver score (5 to 6 points) within 7 days prior to Cycle 1, Day 1. * Has alpha fetoprotein (AFP) concentration lower than 400 ng/mL within 28 days prior to Cycle 1, Day 1. * Has controlled hepatitis B (Hep B). * Has recovered adequately from toxicity and/or complications from the local intervention (surgical resection or local ablation) prior to starting study treatment. * If female, is not pregnant or breastfeeding, and at least one of the following conditions applies: 1) Is not a woman of childbearing potential (WOCBP); or 2) Is a WOCBP and using a contraceptive method that is highly effective or be abstinent from heterosexual intercourse as their preferred and usual lifestyle (a WOCBP must have a negative pregnancy test within 72 hours before the first dose of study treatment). * If undergoing surgical resection, has submitted a tumor tissue sample during S…