Defective Hippo/YAP signaling in the liver results in tissue overgrowth and development of hepatocellular carcinoma (HCC). Here, we uncover mechanisms of YAP-mediated hepatocyte reprogramming and HCC pathogenesis. YAP functions as a rheostat in maintaining metabolic specialization, differentiation, and quiescence within the hepatocyte compartment. Increased or decreased YAP activity reprograms subsets of hepatocytes to different fates associated with deregulation of the HNF4A, CTNNB1, and E2F transcriptional programs that control hepatocyte quiescence and differentiation. Importantly, treatment with small interfering RNA-lipid nanoparticles (siRNA-LNPs) targeting YAP restores hepatocyte differentiation and causes pronounced tumor regression in a genetically engineered mouse HCC model. Furthermore, YAP targets are enriched in an aggressive human HCC subtype characterized by a proliferative signature and absence of CTNNB1 mutations. Thus, our work reveals Hippo signaling as a key regulator of the positional identity of hepatocytes, supports targeting of YAP using siRNA-LNPs as a paradigm of differentiation-based therapy, and identifies an HCC subtype that is potentially responsive to this approach.

According to the clonal model of tumor evolution, trunk alterations arise at early stages and are ubiquitous. Through the characterization of early stages of hepatocarcinogenesis, we aimed to identify trunk alterations in hepatocellular carcinoma (HCC) and study their intra- and inter-tumor distribution in advanced lesions. A total of 151 samples representing the multistep process of hepatocarcinogenesis were analyzed by targeted-sequencing and a single nucleotide polymorphism array. Genes altered in early lesions (31 dysplastic nodules [DNs] and 38 small HCCs [sHCC]) were defined as trunk. Their distribution was explored in: a) different regions of large tumors (43 regions, 21 tumors), and b) different nodules of the same patient (39 tumors, 17 patients). Multinodular lesions were classified as intrahepatic metastases (IMs) or synchronous tumors based on chromosomal aberrations. TERT promoter mutations (10.5%) and broad copy-number aberrations in chromosomes 1 and 8 (3-7%) were identified as trunk gatekeepers in DNs and were maintained in sHCCs. Trunk drivers identified in sHCCs included TP53 (23%) and CTNNB1 (11%) mutations, and focal amplifications or deletions in known drivers (6%). Overall, TERT, TP53 and CTNNB1 mutations were the most frequent trunk events and at least one was present in 51% of sHCCs. Around 90% of mutations in these genes were ubiquitous among different regions of large tumors. In multinodular HCCs, 35% of patients harbored IMs; 85% of mutations in TERT, TP53 and/or CTNNB1 were retained in primary and metastatic tumors. Trunk events in early stages (TERT, TP53, CTNNB1 mutations) were ubiquitous across different regions of the same tumor and between primary and metastatic nodules in >85% of cases. This concept supports the knowledge that single biopsies would suffice to capture trunk mutations in HCC. Trunk alterations arise at early stages of cancer and are shared among all malignant cells of the tumor. In order to identify trunk alterations in HCC, we characterized early stages of hepatocarcinogenesis represented by dysplastic nodules and small lesions. Mutations in TERT, TP53 and CTNNB1 genes were the most frequent. Analyses in more advanced lesions showed that mutations in these same genes were shared between different regions of the same tumor and between primary and metastatic tumors, suggesting their trunk role in this disease.

Portal vein thrombosis (PVT) is a relatively frequent event in patients with cirrhosis. While different risk factors for PVT have been reported, such as decreased portal blood flow velocity (PBFV) and parameters related with severity of portal hypertension, these are based on retrospective studies assessing only a discrete number of parameters. The aim of the current study was to evaluate the incidence and risks factors for non-tumoral PVT development in a large prospective cohort of patients with cirrhosis. We performed an exhaustive evaluation of clinical, biochemical, inflammatory and acquired/hereditary hemostatic profiles in 369 patients with cirrhosis without PVT who were prospectively followed-up. Doppler ultrasound was performed at baseline and every 6 months or whenever clinically indicated. PVT development was always confirmed by computed tomography. Twenty-nine patients developed non-tumoral PVT, with an incidence of 1.6%, 6% and 8.4% at 1, 3 and 5 years, respectively. Low platelet count, PBFV <15 cm/sec and history of variceal bleeding were factors independently associated with a high PVT risk. No relationship between PVT development and any other clinical biochemical, inflammatory and acquired or hereditary hemostatic parameter was found. In patients with cirrhosis, the factors predictive of PVT development were mainly those related to the severity of portal hypertension. Our results do not support the role of hemostatic alterations (inherited or acquired) and inflammatory markers in the prediction of PVT in patients with cirrhosis. Patients with cirrhosis and more severe portal hypertension are at higher risk of non-tumoral portal vein thrombosis development. Acquired or inherited hemostatic disorders, as well as inflammatory status, do not seem to predict the development of portal vein thrombosis in patients with cirrhosis.

Mixed hepatocellular cholangiocarcinoma (HCC-CCA) is a rare and poorly understood type of primary liver cancer. We aimed to perform a comprehensive molecular characterization of this malignancy. Gene expression profiling, DNA copy number detection, and exome sequencing using formalin-fixed samples from 18 patients with mixed HCC-CCA were performed, encompassing the whole histological spectrum of the disease. Comparative genomic analysis was carried out, using independent datasets of HCC (n=164) and intrahepatic cholangiocarcinoma (iCCA) (n=149). Integrative genomic analysis of HCC-CCAs revealed that cholangiolocellular carcinoma (CLC) represents a distinct biliary-derived entity compared with the stem-cell and classical types. CLC tumors were neural cell adhesion molecule (NCAM) positive (6/6 vs. 1/12, p<0.001), chromosomally stable (mean chromosomal aberrations 5.7 vs. 14.1, p=0.008), showed significant upregulation of transforming growth factor (TGF)-β signaling and enrichment of inflammation-related and immune response signatures (p<0.001). Stem-cell tumors were characterized by spalt-like transcription factor 4 (SALL4) positivity (6/8 vs. 0/10, p<0.001), enrichment of progenitor-like signatures, activation of specific oncogenic pathways (i.e., MYC and insulin-like growth factor [IGF]), and signatures related to poor clinical outcome. In the classical type, there was a significant correlation in the copy number variation of the iCCA and HCC components, suggesting a clonal origin. Exome sequencing revealed an average of 63 non-synonymous mutations per tumor (2 mean driver mutations per tumor). Among those, TP53 was the most frequently mutated gene (6/21, 29%) in HCC-CCAs. Mixed HCC-CCA represents a heterogeneous group of tumors, with the stem-cell type characterized by features of poor prognosis, and the classical type with common lineage for HCC and iCCA components. CLC stands alone as a distinct biliary-derived entity associated with chromosomal stability and active TGF-β signaling. Molecular analysis of mixed hepatocellular cholangiocarcinoma (HCC-CCA) showed that cholangiolocellular carcinoma (CLC) is distinct and biliary in origin. It has none of the traits of hepatocellular carcinoma (HCC). However, within mixed HCC-CCA, stem-cell type tumors shared an aggressive nature and poor outcome, whereas the classic type showed a common cell lineage for both the HCC and the intrahepatic CCA component. The pathological classification of mixed HCC-CCA should be redefined because of the new molecular data provided.