Performance of the 7^thand 8^thEditions of the American Joint Committee on Cancer Staging System in Patients with Intraductal Papillary Mucinous Neoplasm-Associated PDAC: A Multi-institutional Analysis

Objective: To validate the 7^thand 8^theditions of the AJCC staging system for patients with invasive carcinomas arising in association with IPMN (IPMN-associated PDAC). Background Data: Although several studies have validated AJCC systems in patients with conventional PDAC, their applicability to IPMN-associated PDAC has not been assessed. Methods: Two hundred seventy-five patients who underwent resection for IPMN-associated PDAC between 1996 and 2015 at 3 tertiary centers and had data on the size of the invasive component and lymph node status were identified. Concordance probability estimates (CPE) were calculated and recursive partitioning analysis was employed to identify optimal prognostic cutoffs for T and N. Results: The CPE for the 7^thand 8^theditions of the AJCC schema were relatively good (0.64 for both) and similar for colloid and tubular subtypes (0.64 for both). The 8^thedition introduced T1a sub-staging and a new distinction between N1 and N2. The utility of the former was confirmed, although the latter did not improve prognostic discrimination. The successful validation of the 8th edition of the AJCC criteria in patients with tubular and colloid subtypes allowed us to compare these patients in early vs late T and N stages which showed that with advanced disease, the prognostic superiority of colloid tumors over their tubular counterparts diminishes. Conclusions: Our findings support the use of the AJCC 8^thedition in the IPMN-associated PDAC population, but suggest that certain cutoffs may need to be revisited. In advanced AJCC stages, patients with colloid vs tubular subtypes have comparable prognosis.