Asynchronous Transitions from Hepatoblastoma to Carcinoma in High-Risk Pediatric Tumors

BackgroundPediatric hepatocellular tumors are most commonly classified as hepatoblastoma (HB) or hepatocellular carcinoma (HCC), yet a subset exhibits mixed histological and molecular features of both. These tumors, previously described as hepatoblastomas with carcinoma features (HBCs), include cases provisionally designated by the World Health Organization as hepatocellular neoplasm-not otherwise specified (HCN-NOS). Their biology remains poorly understood, with unresolved questions about their cellular composition and outcomes. In particular, it is unclear whether HBCs comprise hybrid cell populations with combined HB and HCC characteristics (HBC cells) or admixtures of distinct HB and HCC cells. MethodsWe performed multi-omics profiling--including snRNA-seq, snDNA-seq, and multi-region longitudinal bulk RNA and DNA sequencing--to characterize HBC composition, evolution, and treatment response. ResultsHBCs comprise heterogeneous mixtures of HB-like, HBC-like, and HCC-like molecular cell types. HBC outcomes are significantly worse than HB, and HBC cells are more chemoresistant than HB cells, with resistance shaped by their cell identity, genetic alterations, and embryonic differentiation stage. HBC cells originate from HB cells that were arrested at early hepatic stem cell development stages because of aberrant WNT signaling activation. Inhibition of WNT signaling promoted differentiation and enhanced sensitivity to chemotherapy. Furthermore, each analyzed HBC reflected a dynamic process of multiple HB-to-HBC and HBC-to-HCC transitions, underscoring their evolutionary complexity. ConclusionsMulti-omics profiling of HBCs revealed key findings about their biology and composition, demonstrating that they originate from HB precursors at early hepatic stem cell development stages and that their differentiation arrest depends on sustained aberrant WNT-signaling activity.