GLI1-rearranged mesenchymal tumor of the ovary with a novel ACTG1::GLI1 fusion.

Here, we report an exceedingly rare case of a GLI1-rearranged mesenchymal neoplasm primarily occurring in the ovary, a highly unusual site for this tumor type, which typically arises in the gastrointestinal tract or soft tissues. The patient, a 17-year-old female, presented with acute abdominal pain, and imaging revealed an ovarian mass. Histopathological examination confirmed a GLI1-altered mesenchymal tumor, and RNA sequencing identified a novel ACTG1::GLI1 fusion, representing the first documented case of ACTG1 as a fusion partner for GLI1. By reviewing the literature, we further characterize the morphologic, immunophenotypic, and molecular genetic spectrum of this rare ovarian neoplasm, expanding the known diversity of GLI1-associated fusions in mesenchymal tumors.