Systemic therapy for combined hepatocellular-cholangiocarcinoma: a comprehensive review of chemotherapy, immunotherapy, and targeted therapy.

Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a rare primary liver malignancy exhibiting both hepatocytic and cholangiocytic differentiation. Since the 2019 World Health Organization (WHO) reclassification, growing molecular and clinical evidence has reshaped our understanding of this entity. However, patients with cHCC-CCA have been systematically excluded from landmark clinical trials in both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), leaving clinicians without prospective evidence to guide treatment selection. This review comprehensively evaluates the current evidence on systemic therapy for advanced cHCC-CCA, encompassing cytotoxic chemotherapy, immune checkpoint inhibitors (ICIs), tyrosine kinase inhibitors, and molecularly targeted agents. Retrospective data indicate that gemcitabine plus platinum-based chemotherapy achieves the most consistent efficacy among conventional regimens, with median overall survival of 10-16 months. ICIs demonstrate objective response rates of 20-33% with durable responses in a subset of patients, supported by the finding that approximately 57% of cHCC-CCA tumors harbor an immune-high phenotype. Nearly 25% of tumors carry potentially actionable genomic alterations, including fibroblast growth factor receptor 2 (FGFR2) fusions, isocitrate dehydrogenase 1 (IDH1) mutations, and human epidermal growth factor receptor 2 (HER2) amplification. The molecular heterogeneity of cHCC-CCA, with tumors classifiable as HCC-like or CCA-like in approximately 75% of cases, provides a rational framework for personalized treatment selection. We propose an emerging molecular classification-based treatment algorithm and identify critical gaps requiring dedicated prospective investigation. For clinical settings where comprehensive genomic profiling is not feasible, we discuss a pragmatic surrogate-based approach using imaging characteristics and serum tumor markers to guide initial treatment selection. We also address post-progression treatment considerations, including phenotype-based regimen switching and the role of re-biopsy.