This study is testing a new drug called **ALN-BCAT** for people with a type of liver cancer known as **hepatocellular carcinoma (HCC)**. The study has two parts. In the first part, they are trying to find a safe dose of ALN-BCAT by itself and with another drug called **pembrolizumab**. In the second part, they want to see how well ALN-BCAT works against the cancer. To join, you need to have HCC confirmed by tests, have tried other treatments, and have a specific gene change called a **WNT-pathway mutation**. You cannot join if your cancer is of a certain type or if you have received other treatments recently. They will check if the drug is safe and how well it works.

• Participation requires having previous systemic therapy for advanced cancer.
• The study involves testing ALN-BCAT alone and with pembrolizumab.
• Eligibility includes specific medical conditions and gene mutations.