The Eighth Edition of the American Joint Committee on Cancer Distant Metastases Stage Classification for Metastatic Pancreatic Neuroendocrine Tumors Might Be Feasible for Metastatic Pancreatic Ductal Adenocarcinomas

Background: Significant modifications have been made to the 8th edition of the American Joint Committee on Cancer (AJCC) distant metastases (M) stage classification for metastatic pancreatic neuroendocrine tumors (PanNETs). We aimed to validate this revised classification among metastatic PanNET patients using the Surveillance, Epidemiology, and End Results database. We further sought to evaluate the feasibility of applying this classification to metastatic pancreatic neuroendocrine carcinoma (PanNEC) and pancreatic ductal adenocarcinoma (PDAC) patients. Methods: Stage IV pancreatic neuroendocrine neoplasm (PanNEN, including G1/G2 PanNET and G3 PanNEC classified according to the World Health Organization [WHO] 2010 grading scheme) and PDAC patients with metastatic disease diagnosed between 2010 and 2015 were identified and restaged according to the revised M stage classification for PanNET. Overall survival (OS) was compared using Kaplan-Meier analysis and log-rank test. Uni- and multivariate Cox regression models were utilized to identify prognostic factors. Results: A total of 1,371 stage IV PanNEN and 634 PDAC patients were included. Among PanNEN patients, liver (75.0%) was the most common metastatic site, followed by distant lymph nodes (8.5%), lung (8.4%), bone (7.3%), and brain (1.0%). The 5-year OS for PanNET patients with M1a, M1b, and M1c stage was 44.15, 53.32, and 19.70%, respectively. However, survival comparison showed no significant difference between M1a and M1b stages among PanNET patients. Similar findings were noted after applying this classification to PanNEC patients. Multivariate analysis showed that the age at diagnosis and the number of distant metastatic sites were independent prognostic factors for metastatic PanNEN patients. Interestingly, excellent survival discrimination by M stage among stage IV PDAC patients was noted (M1a vs. M1b vs. M1c, 5-year OS: 5.42, 2.46, and 0%, respectively). Conclusion: Our study is the first large sample-based validation of the AJCC 8th M stage classification for PanNET. The revised classification did not effectively stratify metastatic PanNEN patients. However, further study is warranted to validate this classification for PanNET patients according to the WHO 2017 classification. Interestingly, the revised M stage classification might be feasible for PDAC patients with metastatic disease.