Proposal of a new stage grouping of gastric cancer for TNM classification: International Gastric Cancer Association staging project

Abstract

Background: The current AJCC staging system for gastric cancer (AJCC7) incorporated several major revisions to the previous edition. The T and N categories and the stage groups were newly defined, and adenocarcinoma of the esophagogastric junction (EGJ) was reclassified and staged according to the esophageal system. Studies to validate these changes showed inconsistent results. The International Gastric Cancer Association (IGCA) launched a project to support evidence-based revisions to the next edition of the AJCC staging system.

Methods: Clinical and pathological data on patients who underwent curative gastrectomy at 59 institutions in 15 countries between 2000 and 2004 were retrospectively collected. Patients lost to follow-up within 5 years of surgery were excluded. Patients treated with neoadjuvant therapy were excluded. The data were analyzed in total, and separately by region of treatment.

Results: Of 25,411 eligible cases, 84.8 % were submitted from 24 institutions of Japan and Korea, 6.4 % from other Asian countries, and 8.8 % from 29 Western institutions. The T and N categories of AJCC7 clearly stratified the patient survival. Patients with pN3a and pN3b showed distinct prognosis in all regions, and by introducing pN3a and pN3b into a cluster analysis, we established a new stage grouping with better stratification than AJCC7, especially among stage III subgroups. Survival of Siewert type 2 and 3 EGJ tumors was better stratified by this IGCA stage grouping than by either esophageal or gastric scheme of AJCC7.

Conclusions: For the next revision of AJCC classification, we propose a new stage grouping based on a large, worldwide data collection.

Keywords: AJCC; Gastric cancer; Stage grouping; TNM classifications; UICC.

Figure 1

Overall survival by (a) histological depth of invasion and (b) histological lymph node metastasis.

Figure 2

Stage grouping based on cluster analysis. (a) IGCA stage grouping. Blue-framed categories are different from AJCC-7. (b) AJCC-7 stage grouping.

Figure 3

Patient distribution in Stage IIB and III. The largest proportion of stage III is IIIC by AJCC-7, but is IIIA by IGCA stage grouping.

Figure 4

Survival curves by the stage grouping systems of (a) IGCA proposal and (b) AJCC-7. The IGCA stage grouping widens the distance between the curves especially of stage III subgroups.

Figure 5

Survival curves of Siewert type 2 and 3 esophago-gastric junction tumors by (a) AJCC-7 esophageal system, (b) AJCC-7 gastric system, and (c) IGCA stage grouping. The IGCA stage grouping shows the best separation among the curves.