[Primary ovarian mesonephric-like adenocarcinoma: a clinicopathological analysis of 17 cases].

<b>Objective:</b> To investigate the clinicopathological characteristics, diagnosis, origin, and prognosis of primary ovarian mesonephric-like adenocarcinoma. <b>Methods:</b> A total of 17 cases of primary ovarian mesonephric-like adenocarcinoma diagnosed at the Obstetrics and Gynecology Hospital of Fudan University and Jiaxing Maternal and Child Health Care Hospital between January 2018 and September 2024 were included in this study. Histopathological sections were retrospectively reviewed, and clinicopathological data were systematically analyzed. Immunohistochemical analysis, molecular profiling, and clinical follow-up were performed to further characterize the cases. <b>Results:</b> The patients' age was (57.1±9.3) years. Tumor involvement included 1 bilateral case, 9 left-sided cases, and 7 right-sided cases. Nine cases originated from endometrioid cysts, and 8 cases exhibited coexisting tumor components of other types. Gross examination revealed gray-yellow solid masses or solid components within cysts. Microscopically, the tumors displayed diverse architectural patterns, including papillary, glandular, cystic, tubular, and solid structures, with eosinophilic secretions within glandular lumens and mild to moderate nuclear atypia. Immunohistochemically, the tumors showed variable expression of TTF1, GATA3, CD10, and Calretinin. ER and PR were focally positive in only 2 cases, while others were negative. All cases demonstrated intact DNA mismatch repair proteins expression and wild-type p53 staining patterns. Molecular analysis performed in 10 cases identified pathogenic KRAS mutations in all tested samples. During a follow-up period of 1 to 75 months, 5 cases had recurrence, 1 patient remained alive with disease, and no disease-related death was reported. <b>Conclusions:</b> Ovarian mesonephric-like adenocarcinoma is an aggressive malignancy with a high potential for early recurrence and metastasis. Its frequent association with endometriosis and coexistence with other Müllerian tumors suggest a potential Müllerian origin. The tumor's diverse morphological spectrum and common admixture with other tumor types often pose diagnostic challenges, making it difficult to distinguish from other gynecological malignancies. Therefore, accurate diagnosis of ovarian mesonephric-like adenocarcinoma is crucial for appropriate clinical management and prognostication.