Endoscopic selective muscular dissection for clinical submucosal invasive early gastric cancer

STANDARD TREATMENT FOR clinical submucosal invasive (cT1b) early gastric cancer (EGC) is surgery. Endoscopic submucosal dissection (ESD) can instead be carried out to predict the risk of lymph node metastasis when surgery is against a patient’s will or not feasible as a result of a patient’s age or comorbidities. However, ESD for cT1b EGC often results in a positive vertical margin. Herein, we developed endoscopic selective muscular dissection (ESMD), a new treatment method, to secure the vertical margin. An 80-year-old man presented with a lesion in the posterior wall of the stomach. The lesion had remarkable redness and an uneven surface (Fig. 1). He was diagnosed with cT1b EGC, but strongly refused to undergo surgery; thus, endoscopic resection was carried out. First, in the peripheral part where submucosal invasion was not suspected, circumferential mucosal incision and submucosal dissection were carried out, as done in conventional ESD. In the central part where submucosal invasion was suspected, we identified the oblique muscle layer and the circular muscle layer and then selectively dissected between these muscle layers with the assistance of dental floss clip traction. En bloc resection was achieved without perforation, retaining the circular muscle layer (Video S1). Histopathology showed that the adenocarcinoma invaded the submucosal layer just above the muscle layer, but was resected with negative vertical margin (Fig. 2). In the stomach, the muscularis propria consists of the inner oblique muscle, the middle circular muscle and the outer longitudinal muscle. Their distribution depends on the part of the stomach. Therefore, we should understand the distribution to avoid intraoperative perforation when carrying out ESMD. In addition, as the risk of delayed perforation