Uterine Tumor With Myogenic Differentiation and SRF::RELA Fusion Manifesting as Endometrial Polyp

We report a case of a uterine mesenchymal tumor with myogenic differentiation and SRF::RELA fusion occurring in a 23-year-old woman manifesting as an endometrial polyp. The tumor consisted of bland spindle cells with a predominantly fascicular growth pattern and entrapment of the endometrial glands and vessels. The tumor was positive for smooth muscle markers and CD10. NGS RNA analysis revealed SRF::RELA fusion. NGS DNA analysis revealed no pathogenic variants or copy-number alterations. On follow-up 12 months after curettage, the patient showed no signs of the disease. To the best of our knowledge, only 3 cases of uterine tumors with SRF::RELA fusion arising in the gynecologic tract have been described previously, and all show benign behavior so far. Differential diagnosis includes both benign and potentially aggressive entities, such as leiomyoma, inflammatory myofibroblastic tumor, perivascular epithelioid cell tumor, uterine adenosarcoma, low-grade endometrial stromal sarcoma, and uterine sarcoma with KAT6B/A::KANSL1 fusion.