Hepatocellular Carcinoma (HCC) is a type of liver cancer. This study examines a new treatment called ALN-BCAT to ensure it's safe to use alone and with another medicine, pembrolizumab. The study has two parts: first, finding the best dose; second, checking if it helps fight cancer. Monotherapy means using ALN-BCAT alone, while combining it with pembrolizumab is another approach. Only people with specific conditions can join, like confirmed HCC or certain liver conditions. However, those with certain other liver tumors or who recently had other treatments can't join.

• Participants need to have specific liver cancer types and past treatments.
• The study checks safety and effectiveness of the treatment.
• It's crucial not to have had any cancer therapy recently before joining.