The rationality of N3 classification in the 7th edition of the International Union Against Cancer TNM staging system for gastric adenocarcinomas: a case-control study.

Background: The 7th edition of the International Union Against Cancer/American Joint Committee on Cancer (UICC/AJCC) tumor-node-metastasis (TNM) classification system for gastric cancer is more detailed than the 6th edition with respect to tumor depth and lymph node metastasis. The purpose of this study was to evaluate the rationality of the 7th UICC/AJCC TNM classification system, focusing on N3 gastric cancers.

Methods: A total of 338 patients with N3 gastric cancer who underwent curative resection with ≥ 16 retrieved lymph nodes at two institutions between January 1997 and December 2007 were included in this study. Patients were divided into the N3a (n = 210) and N3b (n = 128) groups. Clinicopathologic characteristics and survival rates were compared between groups.

Results: No difference in clinicopathologic characteristics, including age (p = 0.989), sex (p = 0.382), tumor location (p = 0.124), surgery type (p = 0.909), depth of invasion (p = 0.313), histologic type (p = 0.111), and Lauren classification (p = 0.491), was observed between patients with N3a and N3b gastric cancer. However, overall survival (OS) rates of patients with N3a gastric cancer were greater than that of patients with N3b gastric cancer (5-year OS, 46% vs. 28%; 10-year OS, 33% vs. 19%; both p < 0.001). Five-year survival rates differed significantly between patients with T3N3a and T3N3b (p = 0.006) sub-stages and between those with T4aN3a and T4aN3b (p = 0.004) sub-stages.

Conclusions: The results of this study support N3 sub-classification for gastric cancers, which warrant differential consideration according to TNM stage.