Abstract: Objective To investigate the clinicopathological characteristics, diagnosis, differential diagnosis and prognosis of undifferentiated embryonal sarcoma of the liver (UESL). Methods A retrospective analysis was collected and analyzed on a case of UESL, which focused on the following aspects: histomorphology, immunohistochemical staining and Clinicopathological manifestations. Meanwhile, the published literatures on UESL were reviewed. Methods The patient was a 5-year-old male child with a massive liver mass measuring 15 cm×11 cm×9 cm. Microscopically, the tumor cells were composed of light-moderate atypia spindle cells or stellate mesenchymal cells. Tissue in the interstitium was obviously loose with mucoid degeneration. Eosinophilic bodies were seen inside or outside the cytoplasm. Multinucleated or gigantiform cells could often be seen. Tumor cells were positive for Vimentin, Bcl-2, CD99, CD10, CK7, and Desmin. Eosinophilic bodies were positive for PAS. Ki67 positive index was 60%. Conclusion UESL is a highly malignant tumor composed of originally undifferentiated mesenchymal cells of the liver, most commonly occurred in children. It is necessary to differentiate UESL from hepatoblastoma, hepatic embryonal rhabdomyosarcoma, hepatic mesenchymal hamartoma, and gastrointestinal stromal tumor.

Key words: Undifferentiated embryonal sarcoma of the liver, Immunohistochemistry, Clinicopathological features, Differential diagnosis