Nature Medicine, Published online: 24 November 2025; doi:10.1038/s41591-025-03995-y In this phase 1 trial, treatment of patients with fibrolamellar hepatocellular carcinoma with a therapeutic peptide vaccine targeting the fusion kinase DNAJB1–PRKACA, which is the driver of the disease, together with nivolumab and ipilimumab, was safe and led to encouraging preliminary clinical responses, and translational analysis showed activation of immune responses. Nature Medicine, Published online: 24 November 2025; doi:10.1038/s41591-025-03995-y In this phase 1 trial, treatment of patients with fibrolamellar hepatocellular carcinoma with a therapeutic peptide vaccine targeting the fusion kinase DNAJB1–PRKACA, which is the driver of the disease, together with nivolumab and ipilimumab, was safe and led to encouraging preliminary clinical responses, and translational analysis showed activation of immune responses.