Background: Some studies have reported lymph node metastasis (LNM) in early gastric cancer (EGC) cases meeting the expanded criteria for endoscopic resection. Therefore, we investigated whether a minor poorly differentiated carcinoma (PDC) component in the submucosal (SM) layer affects LNM in differentiated EGC. Methods: We performed surgery in 1096 patients with differentiated SM gastric cancer and compared the clinicopathologic features of node-positive (n = 194) and node-negative (n = 902) differentiated SM cancer, with special reference to the portion of PDC component in the SM layer. Results: When we categorized patients by the proportion of PDC component in the SM layer, we found 840 patients had <5 % and 256 patients had ≥5 % PDC components in the SM layer. The ≥5 % group was significantly associated with younger age, female sex, moderate differentiation, deep SM invasion, lymphovascular invasion (LVI), perineural invasion, and LNM. In multivariate analysis, middle third location, moderate differentiation, SM2 invasion, size >2 cm, LVI, and PDC components in the SM layer were independent risk factors for LNM. When we limited the depth of invasion to SM1, the incidence of LNM was significantly higher in the ≥5 % group. On multivariate analysis, tumor size >2 cm, moderate differentiation, LVI positivity, and ≥5 % PDC components in the SM1 layer were independent risk factors for LNM in SM1 cancer. Conclusions: The PDC component in the SM layer of differentiated EGC was an independent risk factor of LNM, which might constitute a supplementary criterion in the expanded indications for endoscopic resection in differentiated EGC.
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