Differential Prognostic Associations of Monocyte-Containing and Traditional Systemic Inflammatory Indices with Overall Survival After Resection or Palliative Bypass for Pancreatic Cancer: A Retrospective Cohort Study

Background/Objectives: Systemic inflammatory indices may differ prognostically between resectable and palliative pancreatic cancer. We compared associations of the aggregate index of systemic inflammation (AISI), systemic inflammation response index (SIRI), neutrophil-to-lymphocyte ratio (NLR), systemic immune-inflammation index (SII), and monocyte-to-lymphocyte ratio (MLR) with overall survival after pancreatic resection or palliative bypass. Methods: This single-center retrospective cohort included 240 patients treated during 2013–2023 (99 resections; 141 palliative bypasses). Indices derived from preoperative blood counts were natural-log transformed, standardized to 1 SD, and entered separately into operative-group-stratified Cox models. Group-specific associations and interactions were estimated. Reconstructed AJCC eighth-edition stage was incorporated only in the resection stratum. Interaction p values were Holm-adjusted. AISI was designated primary and SIRI key secondary. Results: Overall, 215 deaths occurred. Median overall survival was 17.9 months after resection and 5.4 months after palliative bypass. AISI was associated with mortality following bypass (adjusted hazard ratio [HR] per 1-SD increase in ln(AISI), 1.54; 95% confidence interval [CI], 1.28–1.86) but not following resection (HR, 0.97; 95% CI, 0.75–1.25; interaction p = 0.003; Holm-adjusted p = 0.010). SIRI showed corresponding HRs of 1.60 (95% CI, 1.30–1.96) and 0.93 (95% CI, 0.72–1.20), respectively (interaction p = 0.001; Holm-adjusted p = 0.004). Exploratory MLR analysis also showed statistical heterogeneity. SII was associated with mortality following bypass, but its operative-group interaction was not significant. The conventional NLR interaction was also nonsignificant, although model-assumption violations limited its interpretation. The AISI and SIRI findings remained robust in the sensitivity analyses. Conclusions: AISI and SIRI showed statistical heterogeneity in their associations with overall survival between operative groups, with higher values associated with mortality following palliative bypass. These findings do not establish that the operative procedure modifies the underlying biological relationship. The absence of pathological staging in the bypass group leaves potential residual confounding by disease extent. Independent external validation is required before clinical implementation.