Undifferentiated-type early gastric cancer: from margin demarcation to complete resection

Gastric cancer remains a major global health burden, particularly in Asia, where widespread implementation of endoscopic screening has increased the detection of early gastric cancer (EGC). With advances in endoscopic techniques, endoscopic resection (ER), especially endoscopic submucosal dissection, has become the standard treatment for EGC with a negligible risk of lymph node metastasis (LNM). Undifferentiated-type EGC (UD-EGC) is associated with a higher risk of LNM than differentiated-type EGC. However, favorable long-term outcomes can be achieved with curative resection. Despite this, accurate endoscopic detection, characterization, and delineation of UD-EGC remain a challenge because of their subtle morphology and unique growth pattern. Image-enhanced endoscopy, particularly magnifying endoscopy with narrow-band imaging, plays an important role in diagnosis and assessment of the lateral extent of the lesion. In Japan, accumulating evidence, including prospective multicenter trials, has led to the classification of intramucosal UD-EGC ≤2 cm without ulceration, as an absolute indication for ER in the latest clinical guidelines. Short and long-term outcomes after curative ER for UD-EGC are comparable to those after surgical resection. This review summarizes the current literature on the diagnosis and endoscopic management of UD-EGC, providing a comparative overview of differences in endoscopic treatment recommendations among international guidelines.