Clinical and pathological analysis of 17 cases of mesonephric-like adenocarcinoma.

Mesonephric-like adenocarcinoma (MLA) is a rare gynecological malignancy，during diagnosis, it is frequently mistaken for other gynecological malignancies because different development patterns coexist under a microscope. This study aims to provide a more comprehensive understanding of the disease by analyzing the clinical and pathological characteristics, immunohistochemistry, and molecular features of MLA. A retrospective analysis was conducted on 17 patients with mesonephric-like adenocarcinomadiagnosed by the Department of Pathology at Peking University People's Hospital from January 2021 to June 2025. The lesions were subjected to HE staining and immunohistochemical staining, and 10 cases were examined for gene mutations by next generation sequencing. The results of HE staining, immunohistochemical staining, and molecular testing were examined, along with the clinical information and histological characteristics. The age of the patients ranged from 49 to 83 years (median age 62.3 years), with 3 cases occurred in the ovaries and 14 cases in the uterus. 7 patients presented with (postmenopausal) irregular vaginal bleeding, 3 patient was diagnosed with ovarian or endometrial mass detected by ultrasound during a physical examination, 1 patient was diagnosed with complex endometrial hyperplasia during a hysteroscopy, 1 patient was diagnosed after further examination due to an elevated CA199 level, and 1 patient presented with pain from a liver metastasis. The initial symptoms of the remaining 4 cases referred from other hospitals were unknown. The tumor sizes ranged from 1.3 × 0.8 × 0.5 cm to 8.3 × 7.1 × 4 cm, with solid or cystic-solid growth patterns. Immunohistochemistry showed that 12 cases had negative expression of the estrogen receptor (ER) and progesterone receptor (PR). 13 cases showed an inverse expression relationship between TTF-1 and GATA-3. 12 cases showed patchy positive expression for P16, 10 cases had CD10 positive expression at the luminal edge, and 15 cases had P53 expression that was wild-type. 9 of the 10 patients who had genetic testing had mutations in the KRAS gene at codon 12, 3 had mutations in the PTEN gene, 2 had mutations in the CTNNB1, 1 had a TP53 mutation, 1 had a PIK3CA mutation, 1 had a CCND1 mutation, 1 had a CDK6 mutation, 1 had a BCL2L11 mutation, and 1 had a non-specific molecular profile (NSMP). Mesonephric-like adenocarcinoma is a rare type of gynecologic malignant tumor. Because of its complex histomorphology, pathologists have to distinguish it from other gynecological tumors during diagnosis. The expression of TTF-1, GATA-3, and CD10 in immunohistochemistry can assist the diagnosis. Apart from immunohistochemical indicators, MLA is frequently linked to gene mutations like KRAS, TP53, and CTNNB1, which can aid pathologists in their diagnosis. MLA can spread to distant locations such the pelvis, liver, spleen, and colon, and it has a bad prognosis. To enable patients to obtain additional treatment in a timely way, pathologists must improve the diagnostic accuracy of this disease. An uncommon form of gynecological cancer, Mesonephric-like adenocarcinoma was added to the World Health Organization's (WHO) 5th edition of the classification of cancers of the female reproductive system in 2020. In regular clinical practice, it is comparatively rare. We gathered 17 Mesonephric-like adenocarcinoma cases for this study and compiled the clinical data, such as patient age at onset, initial symptoms, surgical techniques, recurrence or prognosis, and histopathological features like immunohistochemical expression, molecular features, and hematoxylin-eosin (HE) staining characteristics.The aim is to raise pathologists' awareness of this uncommon illness, avoid missing or incorrect diagnosis throughout the diagnostic process.