Mesenterico-portal vein invasion should be an important factor in TNM staging for pancreatic ductal adenocarcinoma: Proposed modification of the 8th edition of the American Joint Committee on Cancer staging system

BACKGROUND The 8th edition of the American Joint Committee on Cancer (AJCC) staging system for pancreatic ductal adenocarcinoma (PDAC) excludes extrapancreatic extension from the assessment of T stage and restages tumors with mesenterico-portal vein (MPV) invasion into T1-3 diseases according to tumor size. However, MPV invasion is believed to be correlated with a poor prognosis. AIM To analyze whether the inclusion of MPV invasion can further improve the 8th edition of the AJCC staging system for PDAC. METHODS This study retrospectively included 8th edition AJCC T1-3N0-2M0 patients undergoing pancreaticoduodenectomy/total pancreatectomy from two cohorts and analyzed survival outcomes. In the first cohort, a total of 7539 patients in the surveillance, epidemiology, and end results database was included, and in the second cohort, 689 patients from the West China Hospital database were enrolled. RESULTS Cox regression analysis showed that MPV invasion is an independent prognostic factor in both databases. In the MPV- group, all pairwise comparisons between the survival functions of patients with different stages were significant except for the comparison between patients with stage IIA and those with stage IIB. However, in the MPV+ group, pairwise comparisons between the survival functions of patients with stage IA, stage IB, stage IIA, stage IIB, and stage III were not significant. T1-3N0 patients in the MPV+ group were compared with the T1N0, T2N0, and T3N0 subgroups of the MPV-group; only the survival of MPV-T3N0 and MPV+T1-3N0 patients had no significant difference. Further comparisons of patients with stage IIA and subgroups of stage IIB showed (1) no significant difference between the survival of T2N1 and T3N0 patients; (2) a longer survival of T1N1 patients that was shorter than the survival of T2N0 patients; and (3) and a shorter survival of T3N1 patients that was similar to that of T1-3N2 patients. CONCLUSION The modified 8th edition of the AJCC staging system for PDAC proposed in this study, which includes the factor of MPV invasion, provides improvements in predicting prognosis, especially in MPV+ patients.