Background: Even though indications for endoscopic resection (ER) in early gastric cancer are determined based on the potential risk of lymph node metastasis, the criteria for ER remain controversial. Sentinel node (SN) mapping for early gastric cancer can help determine regional lymphatic flow patterns. The aim of this study was to assess lymphatic flow according to the SN concept in patients with early gastric cancer, especially those who satisfy the expanded criteria for ER. Methods: We retrospectively enrolled 301 patients diagnosed with pT1 adenocarcinoma who had undergone gastrectomy with SN mapping and had no lymphovascular invasion. Patients were categorized into six groups based on oncological assessment. We analyzed lymphatic flow, including the number of identified SN and SN basin, and the rate of SN metastasis in each group. Results: Of the 301 patients, 128 (42.5%) met the criteria for ER, with 18 in the absolute group and 110 in the expanded group; 173 (57.5%) were assigned to the surgical group. SN metastasis rate tended to be higher in surgical group patients than in ER criteria patients. In the expanded criteria group, the sub-group of patients with intramucosal, undifferentiated adenocarcinoma measuring 20 mm or less had a significantly greater number of identified SNs (p = 0.013) and SN basins (p = 0.032). Furthermore, SN metastasis was observed only in this group. Conclusions: Patients with intramucosal, nonulcerated, undifferentiated adenocarcinoma measuring 20 mm or less could develop a lymphatic network. For these patients, careful follow-up is required after ER.
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