Early gastric cancer with lymphoid stroma presenting as a subepithelial lesion diagnosed by endoscopic submucosal dissection

A 53-year-old man underwent an esophagogastroduodenoscopy that showed a 20-mm subepithelial lesion in the middle gastric body. Endoscopic ultrasound revealed a hypoechoic mass located in the submucosa. Biopsy specimens revealed a benign gastric mucosa with severe lymphocytic infiltration in the submucosa. Malignant lymphoma or gastric cancer with lymphoid stroma was suspected. We performed endoscopic submucosal dissection for definitive diagnosis. Histological examination showed undifferentiated adenocarcinoma, which showed positive Epstein–Barr virus-encoded RNA in situ hybridization results, invading the submucosa mixed with dense lymphocytic infiltration. Thus, Epstein–Barr virus-positive gastric cancer with lymphoid stroma was diagnosed. Gastric cancer with lymphoid stroma is a rare subtype of gastric cancer, which is associated with Epstein–Barr virus infection; it sometimes appears as a subepithelial lesion, which makes it difficult to diagnose using standard biopsy. Endoscopic submucosal dissection was useful in obtaining a sufficient tissue for full histological assessment, including immunostaining.