Undifferentiated Embryonal Sarcoma of the Liver With Rhabdoid Morphology Mimicking Carcinoma: Expanding the Morphologic Spectrum or a Distinct Variant?

Undifferentiated embryonal sarcoma of the liver (UESL) is a rare aggressive neoplasm that occurs predominantly in children. Like mesenchymal hamartoma of the liver (MHL), UESL harbors recurrent rearrangements involving 19q13.3 and 19q13.4, a region of the genome that contains a primate-specific cluster of micro-RNAs. Here, we present a case of a high-grade neoplasm that arose in the left hepatic lobe of a 5-year-old male and gave rise to widespread lymph node, visceral, and soft tissue metastases. The tumor was composed of sheets, tubules, and papillae of epithelioid cells with rhabdoid morphology. INI1 and BRG1 expression were retained. Tumor cells diffusely expressed epithelial markers, including multiple keratins. While the morphologic and immunophenotypic features were suggestive of poorly differentiated carcinoma with rhabdoid features, the tumor was found to harbor the t(11;19)(q13;q13.3) translocation characteristic of UESL, as well as a mutation. Given the clinical presentation, imaging, clinical course, the tumor was classified as UESL with unusual, carcinoma-like histopathologic features. In the context of an unclassified high-grade hepatic tumor in a young child, molecular or cytogenetic testing for chromosome 19q13 alterations should be considered.