Validation of the american joint commission on cancer (AJCC) 8th staging edition in patients with pancreatic adenocarcinoma: a SEER database analysis

Background: The 8th edition AJCC staging system for pancreatic cancer incorporated several significant changes. We sought to evaluate this staging system and assess its strengths and weaknesses relative to the 7th edition system. Methods: Using the Surveillance, Epidemiology and End Results (SEER) database (2004-2013), 8,960 patients undergoing surgical resection for non-metastatic pancreatic adenocarcinoma were identified. Overall survival was estimated using the Kaplan- Meier method and compared using log-rank tests. Concordance indices were calculated to evaluate the discriminatory power of both staging systems. Cox proportional hazards model were used to determine the impact of T and N classification on overall survival. Results: The concordance index for AJCC 8th staging system (0.60,CI95% 0.59-0.61) was comparable to that for the 7th AJCC staging system (0.59,CI95% 0.58-0.60). Stratified analyses for each N classification system demonstrated diminishing impact of T classification on overall survival with increasing nodal involvement. The corresponding concordance index for N0, N1 and N2 classifications were 0.58 (CI95%:0.55-0.60), 0.53 (CI95%:0.51-0.55), and 0.53 (CI95%:0.50-0.56) respectively. Conclusion: This is the first large-scale validation of the AJCC 8th edition staging system for pancreatic cancer. The revised system provides similar discrimination as compared to the 7th edition system. However, the 8th edition system allows finer stratification of patients with resected tumors according to extent of nodal involvement.