Endometrial gastric (gastrointestinal)-type mucinous adenocarcinoma: Diagnostic criteria, differential diagnosis, and molecular insights.

Endometrial gastric (gastrointestinal)-type mucinous adenocarcinoma (EGMA) is a rare histologic subtype of endometrial carcinoma that is challenging to recognize as a distinct entity. Mucinous differentiation has been observed in endometrial carcinomas since the 1980s. However, the definitive characterization of endometrial carcinomas with mucinous differentiation has been unclear in the past. Since its formal inclusion in the latest 5th edition of the World Health Organization (WHO) Classification of Female Genital Tumors, and with increasing awareness of this rare entity, more case reports and studies on EGMAs have emerged in the recent years. Some studies sought to understand the expression of gastrointestinal immunohistochemical markers in neoplastic and/or normal endometrium, while others performed comprehensive clinicopathologic characterization of EGMAs, including their molecular characteristics. However, there still exist challenges in the diagnosis of EGMA, with considerable overlaps in morphologic features and immunohistochemical phenotype existing between EGMAs and the other differential diagnoses. This review sought to summarize the known clinical presentation, radiological findings and pathologic features of EGMA to date. We also discuss in detail the salient differential diagnoses to consider, and evaluate the utility of immunohistochemistry in the workup of this entity.