Involvement of superior mesenteric vein and superior mesenteric artery is adverse prognostic factors in patients with localized pancreatic ductal adenocarcinoma before and after chemoradiotherapy comparing T category between American Joint Committee on Cancer (AJCC) and Japan Pancreas Society (JPS)

Background: T category for pancreatic ductal adenocarcinoma (PDAC) in the Classification of Pancreatic Cancer by the Japan Pancreas Society (JPS) is quite different from that in the American Joint Committee on Cancer (AJCC). The aim is to compare prognosis in PDAC patients undergoing chemoradiotherapy (CRT) based on T categories of JPS and AJCC, focusing on extrapancreatic extension. Methods: This study involved 344 PDAC patients who underwent CRT from 2005 to 2019. T-category variables were re-evaluated on computed tomography (CT) images before and after CRT. Disease-specific survival (DSS) was compared based on T categories of JPS and AJCC. Multivariate analysis was performed to identify prognostic factors. Results: Based on T categories of the AJCC on CT-scan images before and after CRT, 5-year DSS of T3 (57.1% and 50%) were better than that of T2 (37.4% and 34.6%). This reversed phenomenon was not observed based on the JPS. The involvement of superior mesenteric vein (PVsm1) and superior mesenteric artery (Asm1) were significant prognostic factors before and after CRT. Our new T classification, which introduced PVsm1 and Asm1, reflected well the prognosis of patients undergoing CRT. Conclusions: The PVsm1 and Asm1 may be practical for T category in PDAC patients undergoing CRT.