BACKGROUND Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a rare primary liver cancer with poor prognosis and a lack of reliable markers for prognostic assessment or tailored postoperative therapy. The expression of human epidermal growth factor receptor 2 (HER2) in cHCC-CCA and its potential role in predicting prognosis remain unclear. Therefore, investigating the clinical significance of HER2 and its underlying mechanisms may provide valuable insights to optimize diagnosis and treatm