Clinical Significance of Lymphatic Involvement in Intramucosal (pT1a) Gastric Cancer Resected by Endoscopic Submucosal Dissection

ABSTRACT Background and Aim Lymphatic involvement is sometimes detected during routine examination of intramucosal (pT1a) gastric cancer resected endoscopically. However, its clinical significance and association with the risk of metastasis remain unknown. Methods This was a retrospective cohort study of 6797 consecutive patients with pT1a gastric cancers treated by endoscopic submucosal dissection (ESD) at three institutions in Japan from January 2005 to August 2023. Patients with 49 uncommon‐type gastric cancer types were excluded. The risk of metastasis for pT1a cancers with lymphatic involvement was quantified by comparing lymph node metastasis and/or metastatic recurrence in patient groups who underwent additional surgery post‐ESD or did not undergo surgery but were followed up for > 3 years. Results Among the 6748 pT1a cancers treated by ESD, 41 lesions (0.6%) had histologically confirmed lymphatic involvement. Among the 41 patients, 1 was excluded from the analysis of metastasis risk because the follow‐up period after ESD without additional surgery was ≤ 3 years. Metastasis was identified in 1 of 40 patients analyzed (2.5%; 95% confidence interval [CI] 0.4%–12.9%), and was not detected in any of the 25 patients with pure differentiated‐type lesions (0.0%; 95% CI 0.0%–13.7%). Conclusions The low prevalence of metastasis after ESD for pT1a gastric cancer with lymphatic involvement, particularly in patients with pure differentiated‐type lesions, suggests a low risk of metastatic recurrence.