Abstract

Background Pancreatic ductal adenocarcinoma (PDAC) is the paradigmatic immunotherapy-refractory cancer, with a 5-year survival of approximately 12% and minimal benefit from immune checkpoint blockade (ICB). The dominant mechanistic explanation classifies PDAC as a T cell-excluded “cold” tumor, implying that no functional anti-tumor T cells are available for checkpoint release. Whether this Block-strategy view is correct has not been re-examined under integrated evasion-framework analysis. Methods We applied a previously developed 16-module immune evasion framework to TCGA-PAAD (n=183), integrated with hub-cytokine analysis (IL-10/TGF-β), Kv1.3-immune channelome data, and clinical trial mapping (12,007 trials). Single-cell validation used two independent PDAC cohorts retrieved through TISCH2: PAAD\_CRA001160 (Peng 2019, 35 samples [24 PDAC + 11 adjacent normal], 57,443 cells) and PAAD\_GSE154778 (Lin 2020, 16 samples, 14,953 cells), examined for CD8A, TOX, PRF1, KCNA3, and FAP expression by cell type. Results PDAC scored highest in CAF Wall (z=0.768) and Platelet Cloak (z=0.663) modules; strategy classification yielded Brake — not Block — driven by a positive KCNA3-survival relationship (HR=0.649, 95% CI 0.43–0.97, p=0.037). Single-cell qualitative analysis of TISCH2 violin plots showed that CD8 exhausted T cells (CD8Tex) carried (i) high CD8A, (ii) the highest TOX expression among annotated cell types, (iii) preserved PRF1, and (iv) high KCNA3 expression. FAP was strongly localized to fibroblasts (peak ∼3.0 vs. <0.5 elsewhere). The pattern was reproduced in the second cohort. The optimal three-module attack (MHC restoration + CAF disruption + VEGF blockade) suppressed 10 of 16 evasion modules in silico (62.5%); zero of 370 PDAC immunotherapy trials test this combination. Conclusions PDAC may not be T cell-cold but T cell-trapped: CD8 T cells with intact Kv1.3 channels appear immobilized behind a FAP-positive cancer-associated fibroblast wall. ICB monotherapy is mechanistically insufficient because the brake is engaged on T cells that cannot reach the tumor. The framework predicts that triple-targeted intervention — checkpoint release + CAF wall disruption + vascular normalization — is the minimum effective strategy. This is a hypothesis-generating computational analysis; prospective experimental and clinical validation are required. ### Competing Interest Statement The authors have declared no competing interest. * CAF : cancer-associated fibroblast CD8Tex : CD8 exhausted T cell FAP : fibroblast activation protein HR : hazard ratio ICB : immune checkpoint blockade KCNA3 : potassium voltage-gated channel subfamily A member 3 (Kv1.3) MHC : major histocompatibility complex PDAC : pancreatic ductal adenocarcinoma PD-1 : programmed cell death protein 1 PD-L1 : programmed death-ligand 1 PRF1 : perforin 1 TCGA : The Cancer Genome Atlas TGF-β : transforming growth factor beta TISCH2 : Tumor Immune Single-cell Hub 2 TOX : thymocyte selection associated HMG box VEGF : vascular endothelial growth factor