Abstract: Background and purpose: In the 8th edition of the TNM staging of gastric cancer, extranodal invasion is listed as one of the independent disease registration variables. The positive patients have a higher disease-related mortality and recurrence rate, which is closely related to the poor prognosis. This study explored the relationship between extracapsular lymph node involvement (EC-LNI) and clinicopathological features of gastric cancer, and analyzed its impact on the survival prognosis of gastric cancer patients. Methods: A retrospective study of 2 386 patients with gastric cancer who underwent radical surgery from Jan. 1, 2012 to Jan. 1, 2015 in the Department of External Medicine of the Fourth Hospital of Hebei Medical University was analyzed. The relationship between EC-LNI and clinicopathological characteristics and its effect on the survival of gastric cancer patients were analyzed. Results: Among the 2 386 gastric cancer patients, 333 (13.96%) were EC-LNI (+), and 2 053 (86.04%) were EC-LNI (-). Univariate analysis showed that tumor diameter, histological type, Borrmann classification, depth of invasion pT stage, tumor pTNM stage, Lauren classification, vascular tumor thrombus, nerve invasion, Ki-67 positive ratio and the expressions of serum tumor markers [carcinoembryonic antigen (CEA), carbohydrate (CA)19 -9 and CA72-4] were related to the status of EC-LNI (both P<0.05). The results of multivariate analysis showed that the tumor diameter (P=0.010), histological type (P=0.016), tumor infiltration depth pT staging (P=0.011), tumor pTNM staging (P=0.003), Borrmann type (P=0.032) and vascular tumor thrombus (P=0.022) were all independent risk factors for EC-LNI. Complete follow-up data were received from 2 273 (95.26%) of the 2 386 gastric cancer patients. The 5-year overall survival (OS) rate of the group was 49.32%, and the 5-year disease-free survival (DFS) rate was 44.61%. Among them, the EC-LNI (+) 5-year OS rate was 27.86%, the 5-year DFS rate was 25.39%, and the EC-LNI (-) 5-year OS and DFS rates were 52.87% and 47.79%, respectively. There were statistically significant differences in the 5-year OS rates and DFS rates between the two groups of patients (both P<0.001). Univariate analysis showed that the number of EC-LNI (P=0.000) was related to the prognosis of gastric cancer patients, and mean age, lesion location, tumor diameter, histological type, Borrmann classification, tumor invasion depth pT stage, lymph node metastasis pN stage, tumor pTNM stage, Lauren classification, presence or absence of vascular tumor thrombus, positive rate of Ki-67 and postoperative chemotherapy were also related to prognosis (all P<0.05). Multivariate analysis showed that tumor histology type (P=0.013), depth of invasion pT stage (P=0.020), lymph node metastasis pN stage (P=0.019), tumor pTNM stage (P=0.001), presence or absence of vascular tumor thrombus (P=0.031) and the number of EC-LNI (P=0.001) were independent risk factors that affected the prognosis of patients, and postoperative adjuvant chemotherapy (P=0.003) was a protective factor for patient’s prognosis. Conclusion: EC-LNI is closely related to the tumor stage and prognosis of patients with gastric cancer. The presence or absence of EC-LNI and the number of EC-LNI are risk factors that affect the prognosis of gastric cancer patients.

Key words: Gastric cancer, Extracapsular lymph node involvement, Prognosis, Risk factors