Endoscopic Diagnosis of Gastric Subepithelial Lesions < 20 mm: Current Strategies and Emerging Solutions

Gastric subepithelial lesions (SELs) < 20 mm are frequently identified during routine endoscopy and account for approximately 90% of all SELs. Although most are benign, a substantial proportion represents gastrointestinal stromal tumors (GISTs), which carry malignant potential even at this small size. Histological confirmation is critical for appropriate risk assessment and treatment planning. However, the diagnostic yield of endoscopic ultrasound-guided tissue acquisition (EUS-TA) is limited for SELs < 20 mm due to technical challenges such as lesion mobility and short needle stroke. Mucosal incision-assisted biopsy (MIAB), which enables direct visualization and targeted sampling, has emerged as a practical alternative. This narrative review summarizes current evidence on endoscopic diagnostic approaches for SELs < 20 mm, including both sampling methods (EUS-TA, MIAB) and nonsampling techniques such as contrast-enhanced EUS, elastography, and artificial intelligence (AI)-assisted image analysis. Each modality has distinct advantages and limitations, and selection should be based on lesion characteristics, endoscopist experience, and resource availability. Nonsampling modalities offer complementary information and are expected to become increasingly relevant. A comprehensive understanding of available diagnostic techniques is essential to support accurate clinical decision-making for SELs < 20 mm.