The Spectrum of Fusions Occurring in Non–Smooth Muscle Mesenchymal Uterine Tumors: A Review of the Current Knowledge

Context.— Non–smooth muscle uterine sarcomas are mostly represented by low-grade endometrial stromal sarcoma. However, several other rare, distinct types of uterine sarcoma are recognized, including high-grade endometrial stromal sarcoma, tumors with kinase fusions, uterine tumors resembling ovarian sex cord tumors, soft tissue–type sarcoma, and emerging entities such as KAT6A/B-rearranged tumors. The landscape of uterine sarcomas has changed, mostly because of the increasing knowledge concerning their molecular aberrations. Objective.— To offer a comprehensive review of the literature focusing on fusions occurring in tumors other than smooth muscle mesenchymal uterine tumors with respect to their type, frequency, and overlap between diagnostic categories and entities. Data Sources.— The data were mined from the PubMed/MEDLINE database covering the time period from January 1988 to June 2023. In total, 156 studies focusing on the problematics of fusions occurring in non–smooth muscle mesenchymal uterine tumors were selected, and thus became the basis for this review. Conclusions.— One hundred ten fusions were identified in 703 tumors. The diagnostic significance of the molecular aberrations occurring in these tumors can be unclear in some cases. This can be related to the rare aberrations with a limited number of reported cases. Additionally, even well-known aberrations considered as specific for a certain distinct entity can occur in other lesions, the biological behavior and clinical significance of which can differ substantially.