Increased Expression of Yes-Associated Protein 1 in Hepatocellular Carcinoma with Stemness and Combined Hepatocellular-Cholangiocarcinoma

Combined hepatocellular-cholangiocarcinoma (cHC-CC) and some hepatocellular carcinomas (HCCs) express stemness-related markers, such as epithelial adhesion molecule (EpCAM) and keratin 19 (K19), the expression of which has been reported to be associated with more aggressive behavior therein than in HCCs without. Yes-associated protein 1 (YAP1), a potential oncogene, is known to promote stem cell proliferation. In the present study, YAP1 expression and clinicopathological features were evaluated and compared among three groups comprising 36 HCCs that expressed both EpCAM and K19, 64 HCCs that did not express EpCAM and K19, and 58 cHC-CCs, which consisted of 38 cases of the classical type and 20 cases of the intermediate-cell subtype. YAP1 expression was more frequently noted in EpCAM(+)/K19(+) HCCs (55.6%) and in cHC-CCs (67.2%) than in EpCAM(-)/K19(-) HCCs (17.2%) (P<0.001 for both). In cHC-CCs, YAP1 expression was observed in 63% of classical type cHC-CCs and in 75% of the intermediate subtype; moreover, such expression was correlated with poorer histological differentiation (P = 0.017) and was more frequently noted in transition zones than in HCC areas (P = 0.060). Disease-free and overall survival showed a statistically significant difference among the three groups: disease-free survival was highest for EpCAM(-)/K19(-) HCCs and lowest for cHC-CCs, with EpCAM(+)/K19(+) HCCs falling in between (P<0.05). Overall survival rate was lower in HCCs and cHC-CCs with YAP1 expression compared to those without (P = 0.05), whereas disease-free survival showed no significant difference according to YAP1 expression. Increased YAP1 expression was more frequently found in cHC-CCs and HCCs with stemness than in HCCs without, and a YAP1 pathway is suggested to be involved in the obtainment stemness characteristics in HCCs and cHC-CCs.