Original study: The rescue staging for pancreatic ductal adenocarcinoma with inadequate examined lymph nodes.

BACKGROUND:In previous studies, it's recommended that the lymph node involvement should be evaluated with enough examined lymph nodes (eLNs) in the 8th American Joint Committee on Cancer (AJCC) staging system for pancreatic cancer. This study aims to put forward a rescue staging system for pancreatic ductal adenocarcinoma (PDAC) patients with inadequate eLNs after pancreatoduodenectomy (PD). METHOD:11,224 PDAC patients undergoing PD in The Surveillance, Epidemiology, and End Results (SEER) database were included. Another Ruijin Pancreatic Disease Center (RJPDC) database consisted of 821 patients was utilized for external validation. RESULTS:The proportions of patients with eLNs≥15 were 44.7% and 32.8% in SEER and RJPDC database separately. The rescue staging system was put forward relying on LNR (HR = 1.83, 95% CI 1.74-1.92, P < 0.001) for N staging of eLNs<15 population and pLNs for the rest. The TNM modalities were also rearranged in the rescue system for better survival coordination. The C-index of rescue staging system was 0.638 while that of AJCC 8th staging system was 0.613 in SEER database. Similar phenomena were observed in RJPDC database. Kaplan-Meier analyses revealed reliable internal coherences (SEER: Ib: P = 0.26; IIa: P = 0.063; IIb: P = 0.53; IIIa: P = 0.11. RJPDC:Ib: P = 0.32; IIa: P = 0.66; IIb: P = 0.76; IIIa: P = 0.66) and significant staging efficiency (SEER: P < 0.001; RJPDC: P = 0.002). CONCLUSION:A rescue staging system was put forward regardless of the eLNs number. And the novel system manifested better predictive capacity than 8th AJCC staging system.