Myxoid Lipoblastoma with New Fusion Transcript CHCHD7::PLAG1 in an 18-Month-Old Girl Diagnosed by Target RNA Sequencing: A Case Report

Lipoblastomas are rare, benign tumors arising from embryonic white fatty precursor cells that continue to proliferate in the postnatal period. We present a case of a minimally differentiated lipoblastoma with myxoid features. Our patient was an 18-month-old female with a painless solid tumefaction in the middle third of the right leg. Histopathologically, the nodular tumor mass consisted of lipoblasts embedded in a myxoid stroma. Immunohistochemistry showed strong diffuse positivity for S100, CD34, CD56, NSE and rare Ki67+ cells. FOXO1 polyploidy was detected in 30% of cells by FISH. Using target RNA sequencing, we detected a CHCHD7::PLAG1 fusion gene showing that the first exons of CHCHD7 were fused to either exon 2 or exon 3 of PLAG1. Our case demonstrates that due to the histomorphologic overlaps, the molecular diagnostics can be essential for the confirmation of the diagnosis of lipoblastoma.