Neoadjuvant Therapy-Induced Remodeling in Pancreatic Ductal Adenocarcinoma: Multimodal Spatial Analysis and Prognosis

Neoadjuvant therapy (NAT) is increasingly used for pancreatic ductal adenocarcinoma (PDAC); yet most patients only achieve partial response. Pathological treatment response grading focuses on assessing residual tumor burden, often overlooking changes in tumor microenvironment (TME). To address this gap, we compared tumor cells and TME of 13 NAT-naïve and 23 post-NAT PDACs using integrated spatial pathomics and transcriptomics, with validation in an independent single-cell spatial dataset. NAT significantly reduced tumor burden (14.7%-6.2%, p = 0.004), but systemic comparison of 13 cytomorphometric features of tumor cells alone did not reliably distinguish between naïve and NAT cases. In contrast, NAT profoundly remodeled TME by increasing cancer-associated fibroblast (CAF) and CD8⁺ T cell densities, promoting CD8⁺ T cell-tumor cell proximity and fibrosis, reducing tumor-associated neutrophils, and redistributing tertiary lymphoid structures (TLSs). Spatial transcriptomics shows NAT induced apoptosis, DNA-damage response, and AGC-kinase (S_TK_X) signaling in tumor cells, and upregulated complement pathway, p53 signaling, and cellular senescence program in TME. Cross-platform single-cell spatial analysis revealed decreased regulatory T cells (Treg) and a shift from myofibroblastic (mCAF) to inflammatory CAF (iCAF). Importantly, post-NAT patients with more fibrosis had longer overall survival (p = 0.02), and higher B-cell density showed a favorable trend (p = 0.06). Together, these results suggest that beyond tumor debulking, NAT induces a coordinated TME remodeling characterized by fibroblast reprogramming, matrix fibrosis, and immune spatial reorganization. Incorporating assessment of NAT-induced stromal and immune changes into TRG may improve prognostication and guide more precise therapy in post-NAT PDAC.