A rare case of ovarian adenomyoma with a CTNNB1 mutation in the background of serous cystadenofibroma

Ovarian adenomyoma is an exceedingly rare benign lesion, with limited data describing its clinicopathologic and molecular features. We report a case of a 50-year-old woman with a complex left mass identified on imaging. Radiologic evaluation demonstrated a 7.5 cm cystic lesion with a lobulated enhancing soft tissue component, raising concern for a neoplastic process. Surgical resection was performed. Histopathologic examination revealed a composite lesion consisting of adenomyoma arising within a serous cystadenofibroma. The adenomyoma component demonstrated benign endometrial-type glands embedded within a prominent smooth muscle stroma, while the cystadenofibroma component showed characteristic papillary structures lined by benign epithelium within fibromatous stroma. Immunohistochemical studies supported Müllerian differentiation, with stromal cells positive for smooth muscle markers and CD10, and both glandular and stromal components expressing estrogen and progesterone receptors. Targeted amplicon-based next-generation sequencing identified a CTNNB1 mutation in the adenomyoma component, while no pathogenic alterations were detected in the serous cystadenofibroma. This case highlights the potential role of Wnt/β-catenin pathway dysregulation in the pathogenesis of adenomyomatous lesions and expands the limited molecular literature on extrauterine adenomyoma. Recognition of this rare entity is important for accurate diagnosis and improved understanding of its biological behavior.