Comparison of the Sixth and Seventh Editions of the AJCC TNM Classification for Gallbladder Cancer

Abstract

BACKGROUND: This study aimed to compare the seventh edition of the tumor node metastasis (TNM) staging system to the sixth edition to validate its usefulness in predicting prognosis for gallbladder cancer. METHODS: Gallbladder cancer patients were staged according to both the sixth and seventh editions of the American Joint Committee on Cancer (AJCC) staging system. RESULTS: A total of 142 patients underwent cholecystectomy for gallbladder cancer. According to the seventh edition, the survival time of N1 and N2 was different (P = 0.006), and the survival difference between N0 and N1 became significant after excluding cases with no lymph node dissection (P = 0.035). The -2 log likelihoods of the sixth and seventh edition TNM stages were 216.282 and 217.460, respectively, suggesting non-superiority of the seventh edition. Excluding cases with no lymph node dissection resulted in a lower -2 log likelihood score for both editions (sixth, 157.002; seventh, 158.758). CONCLUSIONS: Sufficient lymph node dissection allows better prognostic stratification by application of the AJCC staging system. Even though the new N stage of the seventh edition showed some improvement in predicting prognosis, the overall performance of the seventh edition was not much better than the sixth. Further improvement is needed in the gallbladder cancer staging system.