Merali, N.; Amin, S.; Wu, S.; Hernandez, C. V.; Gao, W.; Chouari, T.; Ragulan, C.; Ps, H.; Bagwan, I.; Karanjia, N. D.; Kumar, R.; Lahiri, R. P.; Pencavel, T. D.; Platt, E.; Riga, A.; Worthington, T. R.; Sunshine, S.; Sivakumar, S.; Sadanandam, A.; Rockall, T. A.; Giovannetti, E.; Gordon-Weeks, A.; Dustin, M. L.; Annels, N. E.; Bashford-Rogers, R.; Frampton, A. E.

Pancreatic ductal adenocarcinoma (PDAC) is characterised by profound immune dysfunction and limited response to immunotherapy. Although tertiary lymphoid structures (TLSs) are associated with improved outcomes, most studies focus on their presence or density, providing limited insight into how their organisation contributes to tumour control. Here, we analyse a unique cohort of treatment-naive PDAC patients enriched for exceptionally rare long-term survivors (LTS, n = 23; >5-year survival) alongside more common short-term survivors (STS, n = 24), enabling direct interrogation of mechanisms underlying durable tumour control. We develop a multi-scale spatial framework integrating multiplex imaging, computational modelling, and transcriptomics to quantify TLS architecture. By modelling TLSs as higher-order immune assemblies, we define their structural states, spatial organisation, assembly rules and tissue context-dependency within the tumour microenvironment. We show that long-term survival is associated with organised, spatially integrated TLSs exhibiting coordinated B and T cell zoning, whereas short-term survival is characterised by disorganised, Treg-enriched, and spatially isolated TLSs, despite similar immune cell abundance. These architectural differences align with transcriptional programmes: LTS tumours display coordinated lymphoid and NF-kB driven chemokine signalling, while STS tumours exhibit inflammation uncoupled from immune organisation. Together, these findings demonstrate that durable anti-tumour immunity in PDAC is defined by coordinated transcriptional, cellular, and spatial organisation, rather than immune presence alone. This study provides a blueprint for structure-informed strategies to reprogram the tumour microenvironment and improve outcomes in PDAC.