[Hepatoblastoma for pathologists in 2025]

Hepatoblastoma is a rare tumor, accounting for less than 1% of childhood cancers. Its incidence is increasing, at approximately 2.16 cases per million per year. Between 80-90% of hepatoblastomas occur in children aged 6 months to 5 years, with a median age of 18 months. The 5-year survival rate is 90% for standard-risk patients and 65 % for high-risk patients. Thanks to broad international collaboration, increasingly precise morphologic and molecular characterization of these tumors has led to a better understanding of tumorigenesis mechanisms and the emergence of new biomarkers. Morphologically, hepatoblastomas are characterized by great heterogeneity, combining epithelial and mesenchymal components with or without teratoid features. While the most common subtypes (fetal epithelial, embryonal epithelial, and osteoid mesenchymal) are well defined morphologically, certain diagnostic challenges remain for pathologists-specifically, the definition of hepatocellular neoplasms not otherwise specified (HCN-NOS), which lie at the interface between hepatoblastoma and hepatocellular carcinoma, and the characterization of undifferentiated small cell components. Pathologists play an essential role in the clinical management of children with hepatoblastoma, and the most precise possible morphological characterization is crucial to advance research on this pediatric tumor.