Risk Factors for Metastasis and Prognosis in Non‐Curative Resection After Endoscopic Submucosal Dissection for Undifferentiated‐Type Early Gastric Cancer in a Nationwide Cohort in Japan

OBJECTIVES: Endoscopic submucosal dissection (ESD) is currently the standard treatment for early gastric cancer (EGC) without risk of lymph node metastasis (LNM). However, it is unclear whether the "eCura system," can be applied to undifferentiated-type EGC after non-curative resection. METHODS: This nationwide, multicenter, retrospective study included consecutive patients that resulted in non-curative resection for undifferentiated-type EGC between January 2011 and March 2019. RESULTS: Overall, 1049 patients were divided into the additional surgery (n = 716) and the follow-up without additional surgery (n = 333) groups. LNM occurred in 6% of the additional surgery group. Tumor size > 30 mm and lymphatic invasion were independent risk factors for LNM upon multivariate logistic regression analyses. The area under the receiver operating characteristic curve (AUC) for the exploratory scoring system (incorporating these risk factors) for LNM prediction was 0.768 (95% confidence interval [CI]: 0.687-0.848) and that for the eCura system was 0.783 (0.703-0.864; p = 0.464). The eCura system was used to stratify the follow-up without additional surgery group according to risk. Five-year cancer-specific survival differed among the low-, intermediate-, and high-risk groups (99.6%, 96.9%, and 60.6%, respectively; p < 0.001). The hazard ratios for cancer recurrence in the intermediate- and high-risk groups were 6.54 (95% CI: 0.41-104.20) and 98.2 (12.10-798.50), respectively (p < 0.001). CONCLUSIONS: Lymphatic invasion and a tumor size > 30 mm are associated with the risk of LNM. Our findings support using the eCura system for risk stratification in undifferentiated-type EGC after non-curative resection.