Adult undifferentiated embryonal sarcoma of the liver with spontaneous tumor rupture and comprehensive molecular profiling: a case report

Background: Undifferentiated embryonal sarcoma of the liver (UESL) is an aggressive malignant mesenchymal neoplasm that occurs predominantly in children and is exceptionally rare in adults. Adult UESL carries a significantly worse prognosis, with 5-year overall survival of approximately 30–48%, and no standardized treatment protocol exists. Case Presentation: A 44-year-old woman presented with progressively worsening abdominal pain. Cross-sectional imaging revealed a large cystic hepatic mass initially suspected to represent biliary cystadenoma, cystadenocarcinoma, complex hepatic cyst or abscess. She underwent left lateral hepatectomy, with intraoperative findings notable for a 17-cm tumor with intralesional hemorrhage, vascular involvement, and intraoperatively confirmed spontaneous tumor rupture into the peritoneal cavity. Histopathologic examination confirmed high-grade undifferentiated embryonal sarcoma with negative surgical margins. The patient received five cycles of adjuvant doxorubicin, ifosfamide, and mesna, which were discontinued due to cumulative chemotherapy-induced anemia and fatigue. Comprehensive molecular profiling identified CDKN2B deletion, MAGE-A4 positivity (2+, 80%), low tumor mutational burden, microsatellite-stable status, equivocal genomic loss of heterozygosity, and predicted HLA-A*02:01 positivity with no other actionable genomic alterations. Surveillance imaging at six months demonstrated no evidence of recurrence. Conclusion: Clinicians and radiologists should maintain a high index of suspicion for UESL when evaluating large cystic hepatic lesions in adults, as diagnostic misclassification is common. This case highlights the prognostic significance of spontaneous tumor rupture and demonstrates that molecular profiling can identify biologically relevant alterations — including MAGE-A4 expression — that could inform future investigational approaches. Collaborative multi-institutional efforts are needed to establish standardized treatment protocols for this rare malignancy.