A Lymph Node Staging System for Gastric Cancer: A Hybrid Type Based on Topographic and Numeric Systems

Abstract

Although changing a lymph node staging system from an anatomically based system to a numerically based system in gastric cancer offers better prognostic performance, several problems can arise: it does not offer information on the anatomical extent of disease and cannot represent the extent of lymph node dissection. The purpose of this study was to discover an alternative lymph node staging system for gastric cancer. Data from 6025 patients who underwent gastrectomy for primary gastric cancer between January 2000 and December 2010 were reviewed. The lymph node groups were reclassified into lesser-curvature, greater-curvature, and extra-perigastric groups. Presence of any metastatic lymph node in one group was considered positive. Lymph node groups were further stratified into four (new N0-new N3) according to the number of positive lymph node groups. Survival outcomes with this new N staging were compared with those of the current TNM system. For validation, two centers in Japan (large center, n = 3443; medium center, n = 560) were invited. Even among the same pN stages, the more advanced new N stage showed worse prognosis, indicating that the anatomical extent of metastatic lymph nodes is important. The prognostic performance of the new staging system was as good as that of the current TNM system for overall advanced gastric cancer as well as lymph node-positive gastric cancer (Harrell C-index was 0.799, 0.726, and 0.703 in current TNM and 0.799, 0.727, and 0.703 in new TNM stage). Validation sets supported these outcomes. The new N staging system demonstrated prognostic performance equal to that of the current TNM system and could thus be used as an alternative.

Fig 1. Classification of lymph node groups based on anatomical location.

Lesser curvature (LC) group (station number 1, 3, and 5, according to Japanese classification), greater curvature (GC) group (station number 2, 4sa, 4sb, 4d, 6), and extra-perigastric (EP) group.

Fig 2. Overall survival for new N stages.

A) patient survival among each combination of status-based lymph node groups, B) patient survival for each new N stage at pN1 (number of metastatic lymph nodes: 1–2), C) patient survival for each new N stage at pN2 (number of metastatic lymph nodes: 3–6), D) patient survival for each new N new stage at pN3 (number of metastatic lymph nodes ≥ 7). LC, lesser-curvature group; GC, greater-curvature group; EP; extra-perigastric group.

Fig 3. Kaplan-Meier curves for overall survival of each staging system.

A) TNM 7^th edition system with substages in Yonsei set, B) new TNM staging system with substages in Yonsei set, C) TNM 7^th edition system with substages in NCC set, D) new TNM staging system with substages in NCC set, E) TNM 7^th edition system with substages in TU set, F) new TNM staging system with substages in TU set. NCC, National Cancer Center in Japan; TU, Tokyo University Hospital in Japan.