[Clinicopathological characteristics and genetic alterations of undifferentiated embryonal sarcoma of the liver in children].

Objective: To investigate the clinicopathological characteristics and genetic alterations of undifferentiated embryonal sarcoma of the liver (UESL). Methods: Three cases of UESL diagnosed in the Department of Pathology, the Third Affiliated Hospital of Sun Yat-sen University from 2020 to 2023 were retrospectively collected. The clinical, histomorphological, immunohistochemical, and genetic profiles were reviewed and analyzed. Results: The cohort comprised of three patients, including one male and two females, aged 7, 9, and 15 years, respectively. Tumor locations were in the right lobe of the liver in two cases, and in both the right and left lobes in one case. One case exhibited tumor rupture with hemorrhage. Gross examination revealed solid tumors in gray-red fleshy appearance, with areas of hemorrhage and necrosis. Microscopically, the tumor was composed of irregularly shaped spindle and polygonal cells arranged in bundles or sheets with varying density, scattered within a myxoid matrix containing giant tumor cells and eosinophilic globules. The tumor cells were positive for Vimentin, CD56, CD68, and bcl-2, with a Ki-67 index of 30%-80%. INI1 expression was retained, while p53 exhibited a mutant pattern. CKpan, CK7, CK19, EMA, HepPar-1, Arginase-1, AFP, CD34, S-100, Myogenin, and MyoD1 were negative. All three cases harbored TP53 missense mutations. Case 1 also showed MDM2 copy number amplification (class Ⅰ mutation), and case 2 exhibited a frameshift mutation in exon 10 of TSC2 (class Ⅱ mutation). Additionally, several class Ⅲ mutations were identified in all three cases. Germline testing for tumor-related genetic variants in case 2 revealed a missense mutation in exon 12 of DICER1, an in-frame insertion mutation in exon 8 of MSH2, and a missense mutation in exon 30 of TSC2. Conclusion: UESL is a rare malignant mesenchymal tumor of the liver, predominantly affecting children, with distinctive clinicopathological features and genetic alterations. TP53 mutations may play a key role in the pathogenesis of this tumor.