Cytopathologic features of mesonephric-like adenocarcinoma in the endometrium and ovary: eight cases and literature review.

Mesonephric-like adenocarcinoma (MLA) is rare and clinically aggressive. Previous studies have characterized the histologic, immunohistochemical, and molecular features of MLA; however, there is limited information regarding its cytological features. We performed a single-institution study of 8 MLAs, focusing on cytological features. The study cohort consisted of 8 MLA cases confirmed by histopathology and molecular analysis. The cytology samples collected from cervicovaginal specimens (6 cases) and peritoneal washings (2 cases). Cytologically, both cervicovaginal specimens and peritoneal washings demonstrated tight three-dimensional clusters of epithelial cells with nuclear overlapping, nuclear grooves, and intranuclear cytoplasmic pseudoinclusions. Additional architectural patterns included papillary formations (8/8 cases), discohesive single-cell components (5/8 cases), trabecular arrangements (5/8 cases), rosette-like structures (5/8 cases), and feathering (2/8 cases). The nuclei were round to oval and hyperchromatic to ground-glass in quality. One case showed spindle-shaped nuclei, and four cases exhibited marked anisonucleosis with identifiable mitoses. Hyaline-like globules were present in 3 cases. Notably, two cases demonstrated nuclear feathering, and tumor cell necrosis (tumor diathesis) was observed in two cases. Next-generation sequencing revealed pathogenic KRAS mutations in 4 MLAs and a pathogenic NRAS (p.Q61K) mutation in 1 MLA. Clinically, one patient succumbed to disease one month and another patient experienced a recurrence at 43 months, whereas the remaining patients had no evidence of disease at 3-24 months of follow-up. MLA displays unique cytomorphologic features and accurate identification of MLA on cytology should prompt confirmatory tests to exclude potential morphologic mimics and ensure appropriate diagnosis.