Three Types of Subepithelial Lesion-Like Gastric Cancer Including a New Entity of Gastric Adenocarcinoma

Gastric subepithelial lesions (SEL) are usually found incidentally during esophagogastroduodenoscopy. Most gastric SELs are benign lesions, such as leiomyoma and pancreatic rests. However, neoplastic lesions including neuroendocrine tumors, gastrointestinal stromal tumors, and certain types of gastric adenocarcinoma (GA), such as the recently WHO-classified fundic gland type adenocarcinoma, may be found. The lack of simple and established diagnostic methods for SEL remains a clinical challenge. Standard biopsy is suboptimal for diagnosis due to the subepithelial location of lesions and is therefore often omitted. Furthermore, guideline-based algorithmic approaches for diagnosing SEL also differ between Japan and the USA. In this case series, we describe three cases of gastric SEL that were subsequently diagnosed as GA. Case 1 was a fundic gland type (chief cell predominant type) adenocarcinoma; Case 2 was a poorly differentiated GA; Case 3 was an advanced GA, found after 4 serial years of endoscopic follow-up for SEL. While standard biopsy led to successful diagnosis in the first 2 cases, no standard biopsy was performed during surveillance in Case 3, making its diagnostic effectiveness unclear. The third case highlights the importance of longitudinal observation for endoscopic mucosal alterations that may suggest certain types of GA. Clinicians should be aware that standard biopsy may play an important role in the evaluation of malignant gastric SEL-like lesions. It is crucial to remain vigilant for surface changes in SEL and not to summarily omit standard biopsy.