Long-Term Outcomes of Endoscopic Submucosal Dissection of Undifferentiated-Type Early Gastric Cancer

Abstract

143 Endoscopic submucosal dissection (ESD) is the standard treatment for the subset of patients with early gastric cancer (EGC) satisfying prespecified criteria. The long-term prognosis following ESD for cases of EGC meeting the ESD criteria (achievement of curative resection) is comparable to that achieved with surgical resection. However, this long-term prognosis comparison categorized by the histology according to the differentiation, especially for undifferentiated-type EGC, has not been well established. In the context of histology, undifferentiated-type EGC generally refers to poorly-differentiated tubular adenocarcinoma, signet-ring cell carcinoma, or poorly cohesive carcinoma. Although undifferentiated-type EGC is included among the expanded indications of ESD, the rate of curative resection remains low, reported previously as 61.4% in a meta-analysis and 36.4% in a nationwide cohort study in Korea. This implies that an unmet need persists regarding the accurate prediction of curative resection in undifferentiated-type EGC (difficulty in adopting a precise ESD indication). Therefore, proper candidate selection prior to ESD is important. Endoscopists predict the probability of curative resection using the size and shape of the lesion and whether ulcers are present or not. The most fundamental hypothesis is that endoscopic resection can be performed with curative intent for EGCs without lymph node metastasis. Therefore, indications of ESD were established using the combination of factors associated with a negligible lymph-node metastasis rate from the retrospective analysis of surgically resected specimens. These indications are categorized as per the histology of EGC according to the differentiation, size, and morphologic conditions of the involved lesion. However, optical endoscopic determination of the factors stated above involves operator-dependent characteristics. In the study of a Korean multicenter registry of ESD for undifferentiated-type EGC, there was a discrepancy between pre-ESD indications and post-ESD criteria in 36.7% of all lesions. The underestimation of the size was the most common reason for non-curative resection (71.4%), followed by the underestimation of the invasion depth (32%) and unpredictability of lymphovascular invasion (14.9%). Undifferentiated-type EGC has distinctive growth patterns relative to differentiated-type EGC. Undifferentiated-type EGC is known to extend laterally along the proliferative zone in the intermediate layer of the mucosa (subepithelial spreading), and the development pattern from the intermediate layer could lead to non-exposure to the surface mucosa, limiting the precise measurement of the size of the lesion. Subepithelial-spreading signet-ring cell carcinoma is more prevalent than the epithelial-spreading type in cases with background COMMENTARY