Single-cell multiomics reveals the interplay of clonal evolution and cellular plasticity in hepatoblastoma.

Hepatoblastomas (HB) display heterogeneous cellular phenotypes that influence the clinical outcome, but the underlying mechanisms are poorly understood. Here, we use a single-cell multiomic strategy to unravel the molecular determinants of this plasticity. We identify a continuum of HB cell states between hepatocytic (scH), liver progenitor (scLP) and mesenchymal (scM) differentiation poles, with an intermediate scH/LP population bordering scLP and scH areas in spatial transcriptomics. Chromatin accessibility landscapes reveal the gene regulatory networks of each differentiation pole, and the sequence of transcription factor activations underlying cell state transitions. Single-cell mapping of somatic alterations reveals the clonal architecture of each tumor, showing that each genetic subclone displays its own range of cellular plasticity across differentiation states. The most scLP subclones, overexpressing stem cell and DNA repair genes, proliferate faster after neo-adjuvant chemotherapy. These results highlight how the interplay of clonal evolution and epigenetic plasticity shapes the potential of HB subclones to respond to chemotherapy.

Mutational signature, cancer driver genes mutations and transcriptomic subgroups predict hepatoblastoma survival.

BACKGROUND: Hepatoblastoma is the most frequent pediatric liver cancer. The current treatments lead to 80% of survival rate at 5 years. In this study, we evaluated the clinical relevance of molecular features to identify patients at risk of chemoresistance, relapse and death of disease. METHODS: All the clinical data of 86 children with hepatoblastoma were retrospectively collected. Pathological slides were reviewed, tumor DNA sequencing (by whole exome, whole genome or target) and transcriptomic profiling with RNAseq or 300-genes panel were performed. Associations between the clinical, pathological, mutational and transcriptomic data were investigated. RESULTS: High-risk patients represented 44% of our series and the median age at diagnosis was 21.9 months (range: 0-208). Alterations of the WNT/ß-catenin pathway and of the 11p15.5 imprinted locus were identified in 98% and 74% of the tumors, respectively. Other cancer driver genes mutations were only found in less than 11% of tumors. After neoadjuvant chemotherapy, disease-specific survival and poor response to neoadjuvant chemotherapy were associated with 'Liver Progenitor' (p = 0.00049, p < 0.0001) and 'Immune Cold' (p = 0.0011, p < 0.0001) transcriptomic tumor subtypes, SBS35 cisplatin mutational signature (p = 0.018, p = 0.001), mutations in rare cancer driver genes (p = 0.0039, p = 0.0017) and embryonal predominant histological type (p = 0.0013, p = 0.0077), respectively. Integration of the clinical and molecular features revealed a cluster of molecular markers associated with resistance to chemotherapy and survival, enlightening transcriptomic 'Immune Cold' and Liver Progenitor' as a predictor of survival independent of the clinical features. CONCLUSIONS: Response to neoadjuvant chemotherapy and survival in children treated for hepatoblastoma are associated with genomic and pathological features independently of the clinical features.

Digital Papillary Adenocarcinoma in Nonacral Skin: Clinicopathologic and Genetic Characterization of 5 Cases.

Digital papillary adenocarcinoma (DPA) is a rare sweat gland neoplasm that has exceptionally been reported outside acral locations. Recently, human papillomavirus 42 was identified as the main oncogenic driver of DPA. Herein, we report 5 tumors arising in extra-acral locations predominantly in the female anogenital skin. Four patients were female and 1 patient was male. The mean age at the diagnosis time was 65 years (range: 55 to 82 y). Tumors were located on the vulva (n=3), perianal area (n=1), and forearm (n=1). Histologically, all tumors were lobular and mainly solid and composed of sheets of cells with rare focal papillae and frequent glandular structures in a "back-to-back" pattern and lined by atypical basophilic cells. Immunohistochemistry showed diffuse positivity for SOX10. Epithelial membrane antigen and carcinoembryonic antigen highlighted the luminal cells and staining for p63 and p40 revealed a consistent and continuous myoepithelial component around glandular structures. Follow-up was available in 3 cases (mean duration: 12 mo [range: 8 to 16 mo]). One patient developed local recurrence and 1 experienced regional lymph node metastases. HPV Capture Next-generation sequencing revealed the presence of the HPV42 genome in all samples. Viral reads distributions were compatible in the 5 cases with an episomal nature of the viral genome, with a recurrent deletion in the E1 and/or E2 open reading frames. In conclusion, this study demonstrates that digital DPA may rarely present in nonacral locations mainly in the female anogenital area, usually with a more solid pattern as compared with those cases presenting on the digits and it is also associated with HPV42.

Identification of Modulators of the C. elegans Aryl Hydrocarbon Receptor and Characterization of Transcriptomic and Metabolic AhR-1 Profiles.

The Aryl hydrocarbon Receptor (AhR) is a xenobiotic sensor in vertebrates, regulating the metabolism of its own ligands. However, no ligand has been identified to date for any AhR in invertebrates. In C. elegans, the AhR ortholog, AHR-1, displays physiological functions. Therefore, we compared the transcriptomic and metabolic profiles of worms expressing AHR-1 or not and investigated the putative panel of chemical AHR-1 modulators. The metabolomic profiling indicated a role for AHR-1 in amino acids, carbohydrates, and fatty acids metabolism. The transcriptional profiling in neurons expressing AHR-1, identified 95 down-regulated genes and 76 up-regulated genes associated with neuronal and metabolic functions in the nervous system. A gene reporter system allowed us to identify several AHR-1 modulators including bacterial, dietary, or environmental compounds. These results shed new light on the biological functions of AHR-1 in C. elegans and perspectives on the evolution of the AhR functions across species.

viroCapt: A Bioinformatics Pipeline for Identifying Viral Insertion in Human Host Genome.

INTRODUCTION: The implication of viruses in human cancers, as well as the emergence of next generation sequencing has permitted to investigate further their role and pathophysiology in the development of this disease. One such mechanism is the integration of portions of viral genomes in the human genome, as well as the specific action of viral oncogenes.inding integration sites and preserved oncogenes is still relying on heavy manual intervention. METHODS: We developed an analysis and interpretation pipeline to determine viral insertions. Using data from directed viral capture, the pipeline conducts a crude genotyping phase to select reference viral genomes, identifies chimeric reads, extracts the putative human sequences to locate in the human reference genome, scores and ranks candidate junctions, and exports tabular and visual results. RESULTS: We leverage common bioinformatics tools (bowtie2, samtools, blat), and a dedicated filtering and ranking algorithm, implemented in R, to infer candidate junctions and insertions. Static results (tables, figures) are produced, as well as an interactive interpretation tool developed as a shiny web app. DISCUSSION: We validated this pipeline against published results of HPV, HBV, and AAV2 insertions and show good information retrieval.

Structure, Dynamics, and Impact of Replication Stress-Induced Structural Variants in Hepatocellular Carcinoma.

Oncogene activation leads to replication stress and promotes genomic instability. Here we combine optical mapping and whole-genome sequencing (WGS) to explore in depth the nature of structural variants (SV) induced by replication stress in cyclin-activated hepatocellular carcinomas (CCN-HCC). In addition to classical tandem duplications, CCN-HCC displayed frequent intra-chromosomal and interchromosomal templated insertion cycles (TIC), likely resulting from template switching events. Template switching preferentially involves active topologically associated domains that are proximal to one another within the 3D genome. Template sizes depend on the type of cyclin activation and are coordinated within each TIC. Replication stress induced continuous accumulation of SVs during CCN-HCC progression, fostering the acquisition of new driver alterations and large-scale copy-number changes at TIC borders. Together, this analysis sheds light on the mechanisms, dynamics, and consequences of SV accumulation in tumors with oncogene-induced replication stress. SIGNIFICANCE: Optical mapping and whole-genome sequencing integration unravels a unique signature of replication stress-induced structural variants that drive genomic evolution and the acquisition of driver events in CCN-HCC.

Severe relapse of SARS-CoV-2 infection in a kidney transplant recipient with negative nasopharyngeal SARS-CoV-2 RT-PCR after rituximab.

Immunocompromised patients may experience prolonged viral shedding after their initial SARS-CoV-2 infection, however, symptomatic relapses after remission currently remain rare. We herein describe a severe COVID-19 relapse case of a kidney transplant recipient (KTR) following rituximab therapy, 3 months after a moderate COVID-19 infection, despite viral clearance after recovery of the first episode. During the clinical relapse, the diagnosis was established on a broncho-alveolar lavage specimen (BAL) by RT-PCR. The infectivity of the BAL sample was confirmed on a cell culture assay. Whole genome sequencing confirmed the presence of an identical stain (Clade 20A). However, it had an acquired G142D mutation and a larger deletion of 3-amino-acids at position 143-145. These mutations located within the N-terminal domain are suggested to play a role in viral entry. The diagnosis of a COVID-19 relapse should be considered in the setting of unexplained persistent fever and/or respiratory symptoms in KTRs (especially for those after rituximab therapy), even in patients with previous negative naso-pharyngeal SARS-CoV-2 PCR.

Hepatitis B virus integrations promote local and distant oncogenic driver alterations in hepatocellular carcinoma.

OBJECTIVE: Infection by HBV is the main risk factor for hepatocellular carcinoma (HCC) worldwide. HBV directly drives carcinogenesis through integrations in the human genome. This study aimed to precisely characterise HBV integrations, in relation with viral and host genomics and clinical features. DESIGN: A novel pipeline was set up to perform viral capture on tumours and non-tumour liver tissues from a French cohort of 177 patients mainly of European and African origins. Clonality of each integration event was determined with the localisation, orientation and content of the integrated sequence. In three selected tumours, complex integrations were reconstructed using long-read sequencing or Bionano whole genome mapping. RESULTS: Replicating HBV DNA was more frequently detected in non-tumour tissues and associated with a higher number of non-clonal integrations. In HCC, clonal selection of HBV integrations was related to two different mechanisms involved in carcinogenesis. First, integration of viral enhancer nearby a cancer-driver gene may lead to a strong overexpression of oncogenes. Second, we identified frequent chromosome rearrangements at HBV integration sites leading to cancer-driver genes (TERT, TP53, MYC) alterations at distance. Moreover, HBV integrations have direct clinical implications as HCC with a high number of insertions develop in young patients and have a poor prognosis. CONCLUSION: Deep characterisation of HBV integrations in liver tissues highlights new HBV-associated driver mechanisms involved in hepatocarcinogenesis. HBV integrations have multiple direct oncogenic consequences that remain an important challenge for the follow-up of HBV-infected patients.

Common genetic variation in alcohol-related hepatocellular carcinoma: a case-control genome-wide association study.

BACKGROUND: Hepatocellular carcinoma is a frequent consequence of alcohol-related liver disease, with variable incidence among heavy drinkers. We did a genome-wide association study (GWAS) to identify common genetic variants for alcohol-related hepatocellular carcinoma. METHODS: We conducted a two-stage case-control GWAS in a discovery cohort of 2107 unrelated European patients with alcohol-related liver disease aged 20-92 years recruited between Oct 22, 1993, and March 12, 2017. Cases were patients with alcohol-related hepatocellular carcinoma diagnosed by imaging or histology. Controls were patients with alcohol-related liver disease without hepatocellular carcinoma. We used an additive logistic regression model adjusted for the first ten principal components to assess genetic variants associated with alcohol-related hepatocellular carcinoma. We did another analysis with adjustment for age, sex, and liver fibrosis. New candidate associations (p<1 × 10-6) and variants previously associated with alcohol-related hepatocellular carcinoma were evaluated in a validation cohort of 1933 patients with alcohol-related liver disease aged 29-92 years recruited between July 21, 1995, and May 2, 2019. We did a meta-analysis of the two case-control cohorts. FINDINGS: The discovery cohort included 775 cases and 1332 controls. Of 7 962 325 variants assessed, we identified WNT3A-WNT9A (rs708113; p=1·11 × 10-8) and found support for previously reported regions associated with alcohol-related hepatocellular carcinoma risk at TM6SF2 (rs58542926; p=6·02 × 10-10), PNPLA3 (rs738409; p=9·29 × 10-7), and HSD17B13 (rs72613567; p=2·49 × 10-4). The validation cohort included 874 cases and 1059 controls and three variants were replicated: WNT3A-WNT9A (rs708113; p=1·17 × 10-3), TM6SF2 (rs58542926; p=4·06 × 10-5), and PNPLA3 (rs738409; p=1·17 × 10-4). All three variants reached GWAS significance in the meta-analysis: WNT3A-WNT9A (odds ratio 0·73, 95% CI 0·66-0·81; p=3·93 × 10-10), TM6SF2 (1·77, 1·52-2·07; p=3·84×10-13), PNPLA3 (1·34, 1·22-1·47; p=7·30 × 10-10). Adjustment for clinical covariates yielded similar results. We observed an additive effect of at-risk alleles on alcohol-related hepatocellular carcinoma. WNT3A-WNT9A rs708113 was not associated with liver fibrosis. INTERPRETATION: WNT3A-WNT9A is a susceptibility locus for alcohol-related hepatocellular carcinoma, suggesting an early role of the Wnt-ß-catenin pathway in alcohol-related hepatocellular carcinoma carcinogenesis. FUNDING: Ligue Nationale contre le Cancer, Bpifrance, INSERM, AFEF, CARPEM, Labex OncoImmunology, and Agence Nationale de la Recherche.

Release of infectious virus and cytokines in nasopharyngeal swabs from individuals infected with non-alpha or alpha SARS-CoV-2 variants: an observational retrospective study.

BACKGROUND: The dynamics of SARS-CoV-2 alpha variant shedding and immune responses at the nasal mucosa remain poorly characterised. METHODS: We measured infectious viral release, antibodies and cytokines in 426 PCR+ nasopharyngeal swabs from individuals harboring non-alpha or alpha variants. FINDINGS: With both lineages, viral titers were variable, ranging from 0 to >106 infectious units. Rapid antigenic diagnostic tests were positive in 94% of samples with infectious virus. 68 % of individuals carried infectious virus within two days after onset of symptoms. This proportion decreased overtime. Viable virus was detected up to 14 days. Samples containing anti-spike IgG or IgA did not generally harbor infectious virus. Ct values were slightly but not significantly lower with alpha. This variant was characterized by a fast decrease of infectivity overtime and a marked release of 13 cytokines (including IFN-b, IP-10 and IL-10). INTERPRETATION: The alpha variant displays modified viral decay and cytokine profiles at the nasopharyngeal mucosae during symptomatic infection. FUNDING: This retrospective study has been funded by Institut Pasteur, ANRS, Vaccine Research Institute, Labex IBEID, ANR/FRM and IDISCOVR, Fondation pour la Recherche Médicale.

Transmission of SARS-CoV-2 Alpha Variant (B.1.1.7) From a BNT162b2-Vaccinated Individual.

Cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) acquisition after vaccination with BNT162b2 have been described, but the risk of secondary transmission from fully vaccinated individuals remains ill defined. Herein we report a confirmed transmission of SARS-CoV-2 alpha variant (B.1.1.7) from a symptomatic immunocompetent woman 4 weeks after her second dose of BNT162b2, despite antispike seroconversion.

DNA Methylation Signatures Reveal the Diversity of Processes Remodeling Hepatocellular Carcinoma Methylomes.

BACKGROUND AND AIMS: DNA methylation patterns are highly rearranged in HCCs. However, diverse sources of variation are intermingled in cancer methylomes, precluding the precise characterization of underlying molecular mechanisms. We developed a computational framework (methylation signature analysis with independent component analysis [MethICA]) leveraging independent component analysis to disentangle the diverse processes contributing to DNA methylation changes in tumors. APPROACH AND RESULTS: Applied to a collection of 738 HCCs, MethICA unraveled 13 stable methylation components preferentially active in specific chromatin states, sequence contexts, and replication timings. These included signatures of general processes associated with sex and age but also signatures related to specific driver events and molecular subgroups. Catenin beta 1 mutations were major modulators of methylation patterns in HCC, characterized by a targeted hypomethylation of transcription factor 7-bound enhancers in the vicinity of Wnt target genes as well as a widespread hypomethylation of late-replicated partially methylated domains. By contrast, demethylation of early replicated highly methylated domains was a signature of replication stress, leading to an extensive hypomethylator phenotype in cyclin-activated HCC. Inactivating mutations of the chromatin remodeler AT-rich interactive domain-containing protein 1A were associated with epigenetic silencing of differentiation-promoting transcriptional networks, also detectable in cirrhotic liver. Finally, a hypermethylation signature targeting polycomb-repressed chromatin domains was identified in the G1 molecular subgroup with progenitor features. CONCLUSIONS: This study elucidates the diversity of processes remodeling HCC methylomes and reveals the epigenetic and transcriptional impact of driver alterations.

Genetic alterations of malignant pleural mesothelioma: association with tumor heterogeneity and overall survival.

Development of precision medicine for malignant pleural mesothelioma (MPM) requires a deep knowledge of tumor heterogeneity. Histologic and molecular classifications and histo-molecular gradients have been proposed to describe heterogeneity, but a deeper understanding of gene mutations in the context of MPM heterogeneity is required and the associations between mutations and clinical data need to be refined. We characterized genetic alterations on one of the largest MPM series (266 tumor samples), well annotated with histologic, molecular and clinical data of patients. Targeted next-generation sequencing was performed focusing on the major MPM mutated genes and the TERT promoter. Molecular heterogeneity was characterized using predictors allowing classification of each tumor into the previously described molecular subtypes and the determination of the proportion of epithelioid-like and sarcomatoid-like components (E/S.scores). The mutation frequencies are consistent with literature data, but this study emphasized that TERT promoter, not considered by previous large sequencing studies, was the third locus most affected by mutations in MPM. Mutations in TERT promoter, NF2, and LATS2 were more frequent in nonepithelioid MPM and positively associated with the S.score. BAP1, NF2, TERT promoter, TP53, and SETD2 mutations were enriched in some molecular subtypes. NF2 mutation rate was higher in asbestos unexposed patient. TERT promoter, NF2, and TP53 mutations were associated with a poorer overall survival. Our findings lead to a better characterization of MPM heterogeneity by identifying new significant associations between mutational status and histologic and molecular heterogeneity. Strikingly, we highlight the strong association between new mutations and overall survival.

Recurrent chromosomal rearrangements of ROS1, FRK and IL6 activating JAK/STAT pathway in inflammatory hepatocellular adenomas.

BACKGROUND: Inflammatory hepatocellular adenomas (IHCAs) are benign liver tumours characterised by an activation of the janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway caused by oncogenic activating mutations. However, a subset of IHCA lacks of identified mutation explaining the inflammatory phenotype. METHODS: 657 hepatocellular adenomas developed in 504 patients were analysed for gene expression of 17 genes and for mutations in seven genes by sequencing. 22 non-mutated IHCAs were analysed by whole-exome and/or RNA sequencing. RESULTS: We identified 296 IHCA (45%), 81% of them were mutated in either IL6ST (61%), FRK (8%), STAT3 (5%), GNAS (3%) or JAK1 (2%). Among non-mutated IHCA, RNA sequencing identified recurrent chromosome rearrangement involving ROS1, FRK or IL6 genes. ROS1 fusions were identified in 8 IHCA, involving C-terminal part of genes highly expressed in the liver (PLG, RBP4, APOB) fused with exon 33-35 to 43 of ROS1 including the tyrosine kinase domain. In two cases a truncated ROS1 transcript from exon 36 to 43 was identified. ROS1 rearrangements were validated by fluorescence in situ hybridisation (FISH) and led to ROS1 overexpression. Among the 5 IHCA with FRK rearrangements, 5 different partners were identified (MIA3, MIA2, LMO7, PLEKHA5, SEC16B) fused to a common region in FRK that included exon 3-8. No overexpression of FRK transcript was detected but the predicted chimeric proteins lacked the auto-inhibitory SH2-SH3 domains. In two IHCA, we identified truncated 3'UTR of IL6 associated with overexpression of the transcript. CONCLUSION: Recurrent chromosomal alterations involving ROS1, FRK or IL6 genes lead to activation of the JAK/STAT pathway in IHCAs.

Clinical Impact of Genomic Diversity From Early to Advanced Hepatocellular Carcinoma.

To date, genomic analyses of hepatocellular carcinoma (HCC) have been limited to early stages obtained from liver resection. We aim to describe the genomic profiling of HCC from early to advanced stages. We analyzed 801 HCC from 720 patients (410 resections, 137 transplantations, 122 percutaneous ablations, and 52 noncurative) for 190 gene expressions and for 31 gene mutations. Forty-one advanced HCC and 156 whole exome of Barcelona Clinic Liver Cancer (BCLC) 0/A were analyzed by whole-exome sequencing. Genomic profiling was correlated with tumor stages, clinical features, and survival. Our cohort included patients classified in BCLC stage 0 (9.4%), A (59.5%), B (16.2%), and C (14.9%). Among the overall 801 HCC, the most frequently mutated genes were telomerase reverse transcriptase (TERT) (58.1%), catenin beta 1 (CTNNB1) (30.7%), tumor protein 53 (TP53; 18.7%), AT-rich interaction domain 1A (ARID1A) (13%), albumin (11.4%), apolipoprotein B (APOB) (9.4%), and AXIN1 (9.2%). Advanced-stage HCC (BCLC B/C) showed higher frequencies of splicing factor 3b subunit 1 (SF3B1) (P = 0.0003), TP53 (P = 0.0006), and RB Transcriptional Corepressor 1 mutations (P = 0.03). G1-G6 transcriptomic classification and the molecular prognostic 5-gene score showed different distributions according to the stage of the disease and the type of treatment with an enrichment of G3 (P < 0.0001), poor prognostic score (P < 0.0001), and increased proliferation and dedifferentiation at the transcriptomic level in advanced HCC. The 5-gene score predicted survival in patients treated by resection (P < 0.0001) and ablation (P = 0.01) and in advanced HCC (P = 0.04). Twenty-two percent of advanced HCC harbored potentially druggable genetic alterations, and MET amplification was associated with complete tumor response in patients with advanced HCC treated by a specific MET inhibitor. Conclusion: Genomic analysis across the different stages of HCC revealed the mechanisms of tumor progression and helped to identify biomarkers of response to targeted therapies.

Adeno-associated virus in the liver: natural history and consequences in tumour development.

OBJECTIVE: Adeno-associated virus (AAV) is a defective mono-stranded DNA virus, endemic in human population (35%-80%). Recurrent clonal AAV2 insertions are associated with the pathogenesis of rare human hepatocellular carcinoma (HCC) developed on normal liver. This study aimed to characterise the natural history of AAV infection in the liver and its consequence in tumour development. DESIGN: Viral DNA was quantified in tumour and non-tumour liver tissues of 1461 patients. Presence of episomal form and viral mRNA expression were analysed using a DNAse/TaqMan-based assay and quantitative RT-PCR. In silico analyses using viral capture data explored viral variants and new clonal insertions. RESULTS: AAV DNA was detected in 21% of the patients, including 8% of the tumour tissues, equally distributed in two major viral subtypes: one similar to AAV2, the other hybrid between AAV2 and AAV13 sequences. Episomal viral forms were found in 4% of the non-tumour tissues, frequently associated with viral RNA expression and human herpesvirus type 6, the candidate natural AAV helper virus. In 30 HCC, clonal AAV insertions were recurrently identified in CCNA2, CCNE1, TERT, TNFSF10, KMT2B and GLI1/INHBE. AAV insertion triggered oncogenic overexpression through multiple mechanisms that differ according to the localisation of the integration site. CONCLUSION: We provided an integrated analysis of the wild-type AAV infection in the liver with the identification of viral genotypes, molecular forms, helper virus relationship and viral integrations. Clonal AAV insertions were positive selected during HCC development on non-cirrhotic liver challenging the notion of AAV as a non-pathogenic virus.

BAP1 mutations define a homogeneous subgroup of hepatocellular carcinoma with fibrolamellar-like features and activated PKA.

BACKGROUND & AIMS: DNAJB1-PRKACA fusion is a specific driver event in fibrolamellar carcinoma (FLC), a rare subtype of hepatocellular carcinoma (HCC) that occurs in adolescents and young adults. In older patients, molecular determinants of HCC with mixed histological features of HCC and FLC (mixed-FLC/HCC) remain to be discovered. METHODS: A series of 151 liver tumors including 126 HCC, 15 FLC, and 10 mixed-FLC/HCC were analyzed by RNAseq and whole-genome- or whole-exome sequencing. Western blots were performed to validate genomic discoveries. Results were validated using the TCGA database. RESULTS: Most of the mixed-FLC/HCC RNAseq clustered in a robust subgroup of 17 tumors, which all had mutations or translocations inactivating BAP1, the gene encoding BRCA1-associated protein-1. Like FLC, BAP1-HCC were significantly enriched in females, patients with a lack of chronic liver disease, and fibrotic tumors compared to non-BAP1 HCC. However, patients were older and had a poorer prognosis than those with FLC. BAP1 tumors were immune hot, showed progenitor features and did not show DNAJB1-PRKACA fusion, while almost none of these tumors had mutations in CTNNB1, TP53 and TERT promoter. In contrast, 80% of the BAP1 tumors showed a chromosome gain of PRKACA at 19p13, combined with a loss of PRKAR2A (coding for the inhibitory regulatory subunit of PKA) at 3p21, leading to a high PRKACA/PRKAR2A ratio at the mRNA and protein levels. CONCLUSION: We have characterized a subgroup of BAP1-driven HCC with fibrolamellar-like features and a dysregulation of the PKA pathway, which could be at the root of the clinical and histological similarities between BAP1 tumors and DNAJB1-PRKACA FLCs. LAY SUMMARY: Herein, we have defined a homogeneous subgroup of hepatocellular carcinomas in which the BAP1 gene is inactivated. This leads to the development of cancers with features similar to those of fibrolamellar carcinoma. These tumors more frequently develop in females without chronic liver disease or cirrhosis. The presence of PKA activation and T cell infiltrates suggest that these tumors could be treated with PKA inhibitors or immunomodulators.