Undifferentiated Embryonal Sarcoma of the Liver: A Clinicopathological and Genomic Study of 10 Cases from a Single Institution

Undifferentiated embryonal sarcoma of the liver (UESL) is a rare and aggressive malignancy with limited clinicopathological and genomic characterization. This study aimed to investigate the genomic abnormalities in a cohort of UESL cases. We analyzed ten UESL cases diagnosed at our institution from 2018 to 2025. Tumor specimens underwent DNA and RNA-based next-generation sequencing using the OncoKids® panel, along with chromosomal microarray analysis. The median age at diagnosis was 13.0 years (range: 0.8-18.3), and the median tumor size was 14.4 cm (range: 7.5-26.0). Lung metastases were present in three patients, and six tumors exhibited capsule rupture. Histology revealed pleomorphic, hyperchromatic oval, spindle, or stellate-shaped cells, with CD56 positivity. TP53 was the sole recurring mutated gene, identified in nine of ten cases. Biallelic TP53 inactivation (mutation plus copy number loss, n = 7) correlated with greater chromosomal complexity compared to monoallelic TP53 mutations (n = 2). Segmental gain at 19q13.42-q13.43, including chromosome 19 microRNA cluster (C19MC), was observed only in tumors with biallelic TP53 inactivation. No clinically significant RNA fusions were detected. All patients underwent tumor resection and ARST0332-based chemotherapy; four of six patients with tumor rupture also received whole abdominal radiation. At a median follow-up of 32.0 months (range: 3.0 - 81.2), all nine patients with follow-up were alive. TP53 mutation is a defining molecular event in UESL, with biallelic inactivation linked to increased chromosomal complexity and C19MC locus gain. Despite its aggressive nature, favorable outcomes are achievable with multimodal therapy.