Gastric-Type Extremely Well-Differentiated Adenocarcinoma of the Stomach: A Challenge for Preoperative Diagnosis

Gastric-type extremely well-differentiated adenocarcinoma (EWDA) is a rare type of gastric adenocarcinoma characterized by infiltration of well-formed mucinous glands with little or no nuclear atypia, which resemble foveolar epithelium or pyloric glands. Because of its high degree of differentiation, preoperative biopsy diagnosis of gastric-type EWDA is very difficult. We encountered a case of gastric-type EWDA, manifesting as a Borrmann type 4 lesion, in a 47-year-old man. Despite four repeated biopsies, the preoperative biopsy diagnosis was not conclusive due to the scarcity of diagnostic tumor cells and lack of knowledge regarding the unusual histologic findings of gastric-type EWDA. We herein describe the histologic findings of gastric-type EWDA in detail, with the aim of facilitating a preoperative biopsy diagnosis and understanding of this rare type of gastric adenocarcinoma.