Submucosal Tumor-Like Lesion in Autoimmune Gastritis: A Rare Case of Fundic Gland Type of Gastric Adenocarcinoma

An 86-year-old woman, with no prior medical history, presented with a small submucosal tumor–like lesion on the greater curvature of the lower gastric corpus (Figures A and B) on esophagogastroduodenoscopy. She, without any history of acid secretion inhibitor intake, was diagnosed with autoimmune gastritis (AIG) because of severe atrophic changes in the gastric corpus and the following clinical laboratory results: negative for anti–Helicobacter pylori antibody (no history of H pylori eradication therapy); negative for anti–parietal cell antibody; positive for anti–intrinsic factor antibody; and gastrin, 4900 pg/mL. We decided to perform endoscopic submucosal dissection for this lesion because of a suspicion of neuroendocrine tumor, regardless of no proof on preoperative biopsy. The resected specimen histopathologically showed a gastric adenocarcinoma of the fundic gland (chief cell-predominant) type with negative margin (Figure C). Immunostaining was positive for MUC6 and pepsinogen I (Figure D) and negative for MUC5AC and H+/K+-ATPase. Gastric adenocarcinoma of the fundic gland rarely develops in patients with AIG. Small submucosal tumor–like lesions in AIG are generally more likely to be neuroendocrine tumors. Observation for sporadic neuroendocrine tumor of <1 cm is sometimes acceptable. However, it is recommended to resect small submucosal tumor–like lesion in AIG if the possibility of gastric cancer, such as gastric adenocarcinoma of the fundic gland, cannot be eliminated.