Adult Type Lipoblastoma With a Predominantly Fibroblastic Morphology and a Novel DLEU2::PLAG1 Gene Rearrangement: Two Cases of a Rare Entity

Lipoblastoma is a benign adipocytic lesion with embryonal fat cell differentiation. The tumors most commonly occur in children, however, rare cases have been reported to occur in adults and are generally considered to represent “maturing” or long-standing lipoblastomas. Approximately 60%–80% of these tumors harbor a gene fusion involving the PLAG1 gene, which is known to rearrange with numerous unique fusion partners. Herein, we present two additional cases of so-called maturing lipoblastoma with a review of the literature. Both tumors occurred in adult females and both harbored a yet-unreported DLEU2::PLAG1 fusion transcript. Clinically, both tumors behaved in a benign fashion. The histology was characterized by a prominence of fibroblastic growth with only partial or minimal lipomatous components. This report serves to provide additional characterization of the clinical, histologic, and molecular features of this rare tumor type.