Inclusion criteria:

          1. Participants with hepatocellular carcinoma.

          2. Must have had at least one prior standard-of-care therapy, unless contraindicated.

          3. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.

          4. Must be willing to undergo a biopsy up to 8 weeks before administration of H3B-6527 on
             Cycle 1 Day 1 for part 2 (dose expansion).

          5. Adequate bone marrow and organ function.

        Exclusion criteria:

          1. Uncontrolled significant active infections, except hepatitis B virus (HBV) or
             hepatitis C virus (HCV).

          2. Known human immunodeficiency virus infection.

          3. Presence of gastric or esophageal varices requiring active treatment.

          4. Previous treatment with a selective FGF19-FGFR4 targeted therapy.

          5. Females of childbearing potential, or males who have not had a successful vasectomy,
             who are unable or unwilling to follow adequate contraceptive measures.

          6. Hereditary problems of galactose intolerance, the Lapp lactase deficiency, or
             glucose-galactose malabsorption.