Validation of American Joint Committee on Cancer 8(th) edition of TNM staging in resected distal pancreatic cancer

BACKGROUND: In order to improve risk stratification and clinical management of the pancreatic ductal adenocarcinoma (PDAC), the American Joint Committee on Cancer (AJCC) has published its eighth edition staging manual. Some major changes have been introduced in the new staging system for both T and N categories. Given the rarity of resectable disease, distal pancreatic cancer is likely underrepresented in the published clinical studies, and how the impact of the staging system actually reflects on to clinical outcomes remain unclear. AIM: To validate the AJCC 8(th) edition of TNM staging in distal PDAC. METHODS: A retrospective cohort study was performed in seven academic medical centers in the United States. Clinicopathological prognostic factors associated with progression-free survival (PFS) and overall survival (OS) were evaluated through univariate and multivariate analyses. RESULTS: Overall, 454 patients were enrolled in the study, and were divided into 2 subgroups: Invasive intraductal papillary mucinous neoplasms (IPMN) (115 cases) and non-IPMN associated adenocarcinoma (339 cases). Compared to invasive IPMN, non-IPMN associated adenocarcinomas are more common in relatively younger patients, have larger tumor size, are more likely to have positive lymph nodes, and are associated with a higher tumor (T) stage and nodal (N) stage, lymphovascular invasion, perineural invasion, tumor recurrence, and a worse PFS and OS. The cohort was predominantly categorized as stage 3 per AJCC 7(th) edition staging manual, and it’s more evenly distributed based on 8(th) edition staging manual. T and N staging of both 7(th) and 8(th) edition sufficiently stratify PFS and OS in the entire cohort, although dividing into N1 and N2 according to the 8(th) edition does not show additional stratification. For PDAC arising in IPMN, T staging of the 7(th) edition and N1/N2 staging of the 8(th) edition appear to further stratify PFS and OS. For PDAC without an IPMN component, T staging from both versions fails to stratify PFS and OS. CONCLUSION: The AJCC 8(th) edition TNM staging system provides even distribution for the T staging, however, it does not provide better risk stratification than previous staging system for distal pancreatic cancer.