Context-Dependent Distinct Roles of SOX9 in Combined Hepatocellular Carcinoma–Cholangiocarcinoma

Combined hepatocellular carcinoma-cholangiocarcinoma (cHCC-CCA) is a challenging primary liver cancer subtype with limited treatment options and a devastating prognosis. Recent studies have underscored the context-dependent roles of SOX9 in liver cancer formation in a preventive manner. Here, we revealed that liver-specific developmental <i>Sox9</i> elimination using <i>Alb-Cre;Sox9^(flox/flox)</i> (LKO) and <i>CRISPR/Cas9</i>-based tumor-specific acute <i>Sox9</i> elimination (CKO) in SB-HDTVI-based <i>Akt-YAP1</i> (AY) and <i>Akt-NRAS</i> (AN) cHCC-CCA models showed contrasting responses. LKO abrogates the AY CCA region while stimulating poorly differentiated HCC proliferation, whereas CKO prevents AY and AN cHCC-CCA development irrespective of tumor cell fate. Additionally, AN, but not AY, tumor formation partially depends on the <i>Sox9-Dnmt1</i> cascade. SOX9 is dispensable for AY-mediated, HC-derived, LPC-like immature CCA formation but is required for their maintenance and transformation into mature CCA. Therapeutic <i>Sox9</i> elimination using the <i>OPN-CreERT2</i> strain combined with inducible <i>Sox9</i> iKO specifically reduces AY but not AN cHCC-CCA tumors. This necessitates the careful consideration of genetic liver cancer studies using developmental Cre and somatic mutants, particularly for genes involved in liver development. Our findings suggest that SOX9 elimination may hold promise as a therapeutic approach for a subset of cHCC-CCA and highlight the need for further investigation to translate these preclinical insights into personalized clinical applications.