LAUSR

505 Gastric subepithelial tumor (SET) develops beneath the mucosa or at the extraluminal compression by an intra-abdominal organ. However, majority of gastric SETs are asymptomatic, measuring <10 mm at the time of diagnosis. Therefore, deciding which gastric SETs require additional management remains difficult. Its basic assessment should be performed during the initial endoscopic examination where the SET is first identified. Several endoscopic findings such as the presence of a pillow/cushion sign, certain surface colors (yellowish for lipoma, transparent for cystic lesions, or bluish for vessel structures), or umbilication (suggestive of an ectopic pancreas) are biomarkers indicating a benign lesion. For gastric SETs with these benign endoscopic features, resection is generally unnecessary. However, determining whether a SET is truly benign or has malignant potential such as gastrointestinal stromal tumor, lymphoma, neuroendocrine tumor, metastatic carcinoma, or adenocarcinoma is often difficult; thus, a definitive diagnosis is needed to determine the next management steps. Known high-risk endoscopic characteristics of malignancy include a tumor diameter of ≥20 mm, surface mucosal changes (ulceration or irregular surface), and interval growth between endoscopic examinations. Although an endoscopic ultrasound (EUS) provides important information such as the differentiation between intramural and extramural lesions, tumor size, layer of origin, and echogenicity, its interpretation can be operator dependent. As EUS findings of benign gastric SETs such as leiomyoma, schwannoma, and ectopic pancreas may be similar with that of potentially malignant SETs, such as hypoechoic echotexture and location in the submucosa or muscularis propria layer, the diagnostic accuracy of EUS without tissue acquisition has been unsatisfactory (48%–63.3%). Therefore, a tissue sample should be obtained to diagnose gastric SETs in order to determine the appropriate management. Currently, EUS-guided fine needle aspiration and biopsy (EUS-FNA/B) has been regarded as the gold standard for the tissue acquisition of gastric SETs. The overall diagnostic rate of EUS-FNA/B for gastric SETs has been reported as 74.3%–83.0% with low procedure-related complication rates. The diagnostic adequacy of EUS-FNA/B depends on several factors, including the tumor size, tumor location, endoscopist’s expertise/technique, needle type, and availability of an on-site cytologist. In addition, EUS-FNA/B is not always accessible, especially in resource-limited settings. For these reasons, variCOMMENTARY