A case of gastric-type adenoma with chief cell and parietal cell differentiation surrounded by complete intestinal...

A man in his 70s received Helicobacter pylori eradication therapy after endoscopic submucosal dissection (ESD) of the stomach. A small, yellowish, protuberant lesion was later observed on the anterior wall of the lower body of the stomach on surveillance esophagogastroduodenoscopy. Narrow band imaging-magnified endoscopy showed an irregular pit and net-like vascular pattern, with the background mucosa having a light blue crest pattern. A biopsy was performed, which led to a diagnosis of adenoma with a gastric phenotype, so repeat ESD was performed. The freshly resected specimen showed a small, protuberant, flat lesion with a clear margin, and hematoxylin and eosin staining showed mild architectural and nuclear atypia. The shape of the atypical gland was similar to that of a fundic gland. MUC5AC, MUC6, pepsinogen A, and H⁺/K⁺ ATPase expressions were positive, and CD10 expression was negative, indicating that this tumor could not only differentiate to mucous neck cells but also to chief cells, parietal cells and foveolar epithelium. Therefore, this 4-mm tumor was diagnosed as a type 0-IIa tubular adenoma with fundic gland differentiation. The background mucosa showed complete intestinal metaplasia. Traditionally, gastric-type adenoma has been defined as the pyloric gland-type, but our case had a fundic gland phenotype. Therefore, a new fundic-gland adenoma subtype should be considered in this case.