A Uterine Leiomyoma With a Novel BRAF::ABCB1 t(7; 7)(q34; q21.12) Fusion: A Case Report.

Uterine leiomyomas are the most common benign neoplasms in women, typically driven by mutations in MED12. We report the case of a 68-year-old woman with a history of uterine fibroids who underwent a total laparoscopic hysterectomy. Microscopically, the tumor was a benign-appearing spindle cell neoplasm with focal edema, hyaline plaques, and hemorrhage, but lacking high-grade atypia, tumor cell necrosis, or significant mitotic activity. Immunohistochemistry was consistent with a smooth muscle origin (positive for desmin and smooth muscle actin (SMA), negative for CD10). Due to its unusual features on imaging, next-generation RNA sequencing was performed, which identified a novel BRAF::ABCB1 fusion secondary to t(7;7)(q34;q21.12). This case describes a new, potentially targetable molecular alteration in a uterine leiomyoma, distinct from the common MED12-mutated pathway, highlighting the underlying molecular heterogeneity of these common tumors.