Epithelioid leiomyosarcoma of broad ligament harboring PGR-NR4A3 and UBR5-PGR gene fusions: a unique case report.

A novel molecular subset of epithelioid leiomyosarcomas with rhabdoid features harboring PGR gene rearrangements has recently been documented. Herein, we present a unique case of PGR-rearranged smooth muscle tumor with both PGR-NR4A3 and UBR5-PGR gene fusions reported in a 30-year-old woman who had a mass in the broad ligament. The histological examination showed a round/polygonal to spindle cell tumor with abundant myxoid matrix and focal hyalinization, resulting in an epithelioid pattern. Immunohistochemical examination revealed that the tumor had variable staining for desmin, SMA, and h-caldesmon and diffuse nuclear staining of ER, PR, and WT1. Furthermore, targeted RNA sequencing analysis revealed PGR-NR4A3 and UBR5-PGR gene fusions. Our case in addition with the reported cases suggest that myxoid matrix with two types of tumor cells (round/polygonal epithelioid cells and spindle cells) may be significant for the diagnosis of PGR-NR4A3 fusion-positive leiomyosarcoma. UBR5-PGR gene fusion is a novel finding in epithelioid leiomyosarcoma.