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.

Lipoblastomas are rare, rapidly growing benign tumors rising from embryonic white fatty cells that continue to proliferate in the postnatal period. We presented a case of a toddler with an undifferentiated myxoid neoplasm with features of a minimally differentiated lipoblastoma. 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 lipobastic cells embedded in a myxoid stroma. Immunohistochemistry showed strong diffuse positivity for vimentin, 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 fusion gene, CHCHD7-PLAG1, in the tumor sample. Sequence analysis showed 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 is essential for confirmation of lipoblastomas.