Immunoglobulin G4‐Related Disease‐Like Gastric Lesion Presenting as Submucosal Tumor‐Like Lesions

Immunoglobulin G4 (IgG4)‐related disease (RD) is a systemic fibroinflammatory condition characterized by infiltration of IgG4‐positive plasma cells (PCs). Gastrointestinal involvement may present as submucosal tumor–like lesions and poses diagnostic challenges. We report a case of a 59‐year‐old man with gastric submucosal tumor–like lesions detected during routine screening. Endoscopic submucosal dissection (ESD) was used for the diagnosis and treatment. A histopathological examination revealed abundant IgG4‐positive PC infiltration in the submucosa; however, these findings did not fulfill the comprehensive diagnostic criteria for IgG4‐RD. IgG4‐RD–like gastric lesions can mimic submucosal tumors. ESD may provide diagnostic and therapeutic benefits when a conventional biopsy is insufficient. Cautious interpretation of IgG4‐positive PC infiltration in gastrointestinal specimens is required.