Impact of extra-nodal metastasis on survival in gastric cancer patients with lymph node involvement.

Abstract

57 Background: Extra-nodal metastasis (ENM) is defined as a tumor nodule without lymph node structure, and distinguished from lymph node metastasis by histological findings. Despite the possible difference in metastatic mechanism, both are counted as metastasized lymph nodes according to the 3rd English edition of Japanese Classification of Gastric Carcinoma, and thus the prognostic value of ENM remains unclear. The aim of this study was to clarify the clinicopathogical characteristics and prognostic impact of ENM in gastric cancer patients with lymph node involvement. Methods: This study included 388 patients who underwent curative gastrectomy for primary gastric cancer between January 2009 and August 2013. A total of 2093 pathologically positive tumor nodules, including both metastatic lymph nodes and ENM, were examined. Clinicopathological characteristics and survival outcomes were compared between an ENM positive (ENMP) group (95 patients) and an ENM negative (ENMN) group (293 patients). In addition, multivariable analysis was performed to clarify the independent prognostic factors. Results: ENM was found in 269 of 2093 tumor nodules (12.9 percent). The incidence of ENM was significantly higher in patients with large tumor size, high pathological T stage (pT), high pathological N stage (pN) and in those with macroscopic infiltrative tumors, vascular and lymphatic invasion. Three-year relapse free survival was significantly worse in the ENMP group (56.5%) than in the ENMN group (82.4%, p < 0.001). Multivariable analysis revealed that ENM as well as age, pT and histological type was an independent prognostic factor. Conclusions: ENM is an independent prognostic factor in gastric cancer patients with lymph node involvement. A new N classification stratified by the presence of ENM might be considered.