Calcifying Nested Stromal-Epithelial Tumor of the Liver: A Rare Find

Abstract Introduction/Objective Calcifying Nested Stromal-Epithelial Tumor (CNSET) is a rare tumor of the liver with less than 40 cases described in the literature. It is a low-grade tumor characterized by a distinctive nested architecture surrounded by a cellular myofibroblastic stroma and psammomatous calcifications. CTNNB1 gene deletions have been identified in several cases. CNSET typically arises in the right lobe and there is a female predominance with a predilection for children, adolescents, and young adults. Methods/Case Report We report an interesting case of CNSET in a 13-year-old male with no pertinent medical history who presented with a one-month history of fatigue, paleness, and liver mass on physical examination. MRI abdomen showed a 9.8 cm heterogenous mass with a central scar involving the right lobe of the liver, radiologically favored to be fibrolamellar hepatocellular carcinoma. AFP levels were normal. The patient underwent a partial hepatectomy. On gross examination, the specimen showed a yellow, circumscribed, firm mass. H&E slides showed scattered round to oval nests of bland spindle and epithelioid cells arranged in short fascicles at the periphery of nests. Collagenous stroma surrounding the nests showed spindle cells with tapered nuclei and pinpoint nucleolus. Areas with calcification and osseous metaplasia were also present. Immunohistochemistry performed showed the tumor cells to be positive for pan-cytokeratin (weak), WT-1, and vimentin, and negative for Hepar-1, arginase-1, synaptophysin, chromogranin, S100, NUT-1, myogenin, and desmin. Beta-catenin showed nuclear and cytoplasmic staining pattern. INI-1 was retained within the tumor cells and Ki-67 showed a proliferative index of approximately 10-20%. On MSK-Impact (next- generation sequencing), a mutation in CTNNB1 was detected. Archer FusionPlex was negative for gene fusions within the tumor. Results (if a Case Study enter NA) NA Conclusion It is crucial to become familiar with this rare entity and to avoid mistaking it for hepatoblastoma. CNSET exhibits a biphasic morphology characterized by a nested architecture featuring bland and uniform epithelioid and spindle cells, surrounded by a cellular myofibroblastic stroma. Confirming the diagnosis can be aided by nuclear β- catenin and the expression of WT1.