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

Yoon Young Choi,Jae-Ho Cheong,Woo Jin Hyung,Dong Wook Kim,Ji Yeong An,Yasuhiro Okumura,Sung Hoon Noh,Hyoung-Il Kim,Takeo Fukagawa,Hitoshi Katai,Yasuyuki Seto,Anthony W.I Lo

doi:10.1371/journal.pone.0149555

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.

Highlights

In the field of gastric cancer, the fifth most common cancer and a major leading cause of cancer-related deaths worldwide [1] and in East Asia [2,3], the application of appropriate staging systems has been a widely discussed issue in both Eastern and Western countries
Regardless of the number of metastatic lymph node (LN), if any metastatic LN was involved in one group, we considered the corresponding group to be positive for metastasis
Baseline characteristics were similar to the original set, except for the extent of gastrectomy: pylorus-preserving or proximal gastrectomy cases were more frequently performed in Japan

Summary

Introduction

In the field of gastric cancer, the fifth most common cancer and a major leading cause of cancer-related deaths worldwide [1] and in East Asia [2,3], the application of appropriate staging systems has been a widely discussed issue in both Eastern and Western countries. The staging for the extent of the primary tumor (T stage) is based on the depth of tumor invasion into the gastric wall, the staging for the extent of LN metastasis (N stage) has been converted from an anatomical location—based system to a numeric-based system [5,6]. Within this numeric-based system, the cutoff value of number of metastatic LNs defining the pN category has been changed. The numeric-based N staging system has limitations, including its lack of information on the anatomical extent of the disease and its discordance between preoperative and postoperative N staging [11], as there is no way to determine the number of metastatic LNs prior to an operation; the system cannot represent the extent of LN dissection despite the use of radical LN dissection (D2) as standard treatment [6,12,13]

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