Lymph node metastasis risk according to the depth of invasion in early gastric cancers confined to the mucosal layer

Background: Early gastric cancers (EGCs) within the mucosal layer of the gastric wall have a small risk of lymph node (LN) metastasis. Methods: We reviewed clinicopathology data for patients who underwent surgery for EGC between 2001 and 2013 at the National Cancer Center, Korea. Poisson regression analyses were performed to compare the risk of LN metastasis according to the depth of tumor invasion in patients with mucosal EGCs. Results: Among the 1776 EGC patients included, 580 (32.7 %) had tumors confined to the lamina propria (LP; LP group) and 1196 (67.3 %) had tumors invading the muscularis mucosae (MM; MM group). Seventy-one patients (4.0 %) had LN metastasis, and the MM group had a significantly higher rate of LN metastasis (59 patients, 4.9 %) than the LP group (12 patients, 2.1 %; P = 0.004). A multivariate analysis showed that tumors invading the MM (adjusted risk ratio 1.95; P = 0.045) were significantly associated with LN metastasis in addition to well-known risk factors, including tumor size greater than 3 cm, presence of ulceration, undifferentiated histologic type, and lymphovascular invasion. The incidence of LN metastasis was 1.87 % (95 % confidence interval 0.23–6.59 %) within tumors invading the MM that met the expanded criterion for endoscopic resection of differentiated histologic type of size 3 cm or smaller with ulceration. LN metastasis was not found in tumors meeting the absolute criteria for endoscopic resection. Conclusions: EGCs invading the MM had a higher rate of lymph node metastasis than those confined to the LP. Further study is needed to evaluate whether different curative treatment criteria are needed for LP-confined and MM-invading EGCs.