Endometrial cytological findings for a mesonephric‐like endometrial adenocarcinoma: A case report

Abstract A mesonephric‐like endometrial adenocarcinoma (ML‐EAC) is very rare and has a worse prognosis than other endometrial carcinomas. We describe an ML‐EAC and report our endometrial cytological findings. A 76‐year‐old woman presented with irregular genital bleeding and a uterine mass. Endometrial cytology revealed atypical cylindrical or spindle‐shaped cells in the form of small aggregates or solitary cells. The cell aggregates exhibited irregularly stacked papillary structures, small glandular structures, and fenestrated structures. The atypical cells had a nucleus with fine‐granular chromatin and a granular cytoplasm, and nuclear grooves and intranuclear pseudo‐inclusions were present. Hyaline globules were observed in the glandular lumens and in the background. The presumptive histological type was an adenocarcinoma, but the cytological features were different from those of an endometrioid carcinoma. A histological examination of the endometrial biopsy revealed an adenocarcinoma, and a simple hysterectomy was performed. A grayish‐white elevated mass measuring 90 mm × 70 mm × 40 mm was observed on the uterine corpus in the hysterectomy specimen. Histologically, the tumor proliferated as complex tubular structures containing eosinophilic colloid‐like materials and trabecular structures. The tumor cells were diffuse and positive for GATA‐3 and partially positive for thyroid transcription factor‐1. Estrogen and progesterone receptors were negative. An ML‐EAC was diagnosed. The tumor was invasive and extended beyond one‐half of the muscle layer with a high degree of vascular invasion. In conclusion, we need to focus on the various shapes of the cell aggregate, nuclear grooves, and intranuclear pseudo‐inclusions of tumor cells to distinguish an ML‐EAC from other endometrial carcinomas in endometrial cytology.