Uterine mesenchymal tumour with a novel EWSR1::CTBP1 gene fusion.

A growing number of mesenchymal uterine tumours are defined by a specific molecular aberration. We present the case of a 65-year-old woman who presented with postmenopausal bleeding and a large intramural uterine tumour. Histopathological analysis of the resected uterus revealed an intramural, mesenchymal neoplasm comprising of spindle and epithelioid cells, with no immunohistochemical expression of lineage-specific markers and low proliferative activity. Molecular testing using next-generation sequencing (NGS) revealed an EWSR1::CTBP1 gene fusion, which was confirmed by the presence of EWSR1 gene rearrangement detected using fluorescence in situ hybridisation (FISH). Staging revealed no further tumour manifestations, and the 3-year follow-up was uneventful. The EWSR1::CTBP1 gene fusion has never previously been reported in uterine tumours, having been reported in the literature only once, in the context of a gastroblastoma. The presented case expands the range of the gene-fusion-associated mesenchymal tumours of the uterus.