Mesonephric-Like Adenocarcinoma of the Endometrium: A Rare and Diagnostically Challenging Entity

Mesonephric-like adenocarcinoma (MLA) is a recently recognized and rare entity. It is a morphologically distinctive carcinoma of the uterine corpus, estimated to account for approximately 1% of endometrial malignancies. Its diagnosis is particularly challenging owing to morphological and immunophenotypic overlap with cervical mesonephric adenocarcinoma and other endometrial carcinoma subtypes. Accurate identification has significant clinical implications given its association with aggressive behavior. We report the case of a 62-year-old postmenopausal woman who presented with a two-day history of postmenopausal vaginal bleeding. A PET/MR fusion scan revealed a metabolically active, T2-hyperintense lesion involving the posterior uterine wall and lower uterine segment, associated with haematometra. She underwent a total abdominal hysterectomy with bilateral salpingo-oophorectomy and comprehensive surgical staging. Histopathological examination demonstrated a high-grade carcinoma with tumor cells arranged in small tubules, nests, and sheets, containing intraluminal eosinophilic secretions, a pattern characteristic of mesonephric-like differentiation. Immunohistochemistry showed diffuse positivity for GATA3 and PAX8, with wild-type p53 expression, supporting the diagnosis of MLA. Tumor invasion exceeded 50% of the myometrial thickness (93.75%), with negative lymph nodes and clear surgical margins, yielding a final stage of pT1b pN0 (the International Federation of Gynecology and Obstetrics (FIGO) stage IIC). This report underscores the critical importance of integrating classical morphological assessment with a targeted immunohistochemical panel in diagnosing MLA. As this entity is increasingly recognized, pathologists must maintain a high index of suspicion, particularly in postmenopausal women with tumors exhibiting tubular architecture and eosinophilic luminal secretions.