Incremental Prognostic Information Beyond Nodal Positivity: The AJCC 8th Edition N1/N2 Subdivision and the Lymph Node Ratio in Resected Periampullary Adenocarcinoma

Background/Objectives: The American Joint Committee on Cancer (AJCC) 8th edition subdivides node-positive periampullary adenocarcinoma into N1 and N2 by the number of positive nodes. We quantified how much this subdivision and the lymph node ratio (LNR) each add to nodal positivity, and how the nodal yield affects the comparison. Methods: This retrospective cohort comprised 147 consecutive pancreatoduodenectomies for pancreatic head (n = 49), distal bile duct (n = 63), ampullary (n = 31) or duodenal (n = 4) adenocarcinoma. In covariate-adjusted Cox models stratified by origin, the N1/N2 subdivision and the LNR were tested over nodal positivity and over each other with nested likelihood-ratio tests, overall, with the examined-node count in the model and by the period of resection. Results: The median nodal yield was 17 (10 in 2013–2016, 19 in 2017–2024). Beyond nodal positivity, the N1/N2 subdivision added χ2 0.25 (p = 0.61; adjusted N2-versus-N1 hazard ratio 1.21, 95% confidence interval [CI] 0.59–2.45) and the LNR added χ2 9.60 (p = 0.002; hazard ratio 1.41 per 0.1, 95% CI 1.22–1.62). The LNR added to the N category (p = 0.002; optimism-corrected C-index gain 0.020, 95% CI 0.002–0.041), whereas the N category did not add detectably to the LNR (p = 0.54). With the examined-node count in the model, the LNR increment was attenuated (p = 0.045) and the subdivision’s increment rose (χ2 3.65, p = 0.056). From 2017 onward (n = 113), the LNR and the positive-node count were nearly collinear among the node-positive patients (ρ 0.90 versus −0.02 before 2017), and neither the subdivision (p = 0.49) nor the LNR (p = 0.17) added significantly to positivity. Conclusions: The N1/N2 subdivision added little beyond nodal positivity, although imprecisely estimated, and its increment rose when the examined-node count was in the model. The LNR added prognostic information mainly when the yield was low or variable; where the yield was higher and more uniform, the ratio and the count-based category conveyed nearly the same information, and no additional value of the ratio was demonstrated.