Fibroblast–myeloid stromal crosstalk is associated with clinicopathological diversity in intraductal papillary mucinous neoplasms of the pancreas

Abstract Intraductal papillary mucinous neoplasm (IPMN), a grossly visible precursor of pancreatic ductal adenocarcinoma, is classified into gastric, intestinal, and pancreatobiliary subtypes, each associated with distinct clinicopathological features and biological aggressiveness. We hypothesised that the tumour microenvironment can explain the association between histological subtypes and clinical outcomes. We first enrolled 116 IPMN resection cases, with or without associated invasive carcinoma, and then sequenced four single‐nucleus RNA‐sequencing (snRNA‐seq) libraries from those with distinct histological grades and subtypes. The snRNA‐seq revealed that fibroblasts were the main source of cell–cell communication, whereas myeloid and mast cells were the main receivers. Therefore, we subclassified fibroblasts into inflammatory (iCAF), myofibroblast (myCAF), and reticular‐like (rCAF) subpopulations, and myeloid cells into monocytes, neutrophils, macrophages, and dendritic cell subpopulations. Cell–cell interaction analysis revealed that iCAF and rCAF mainly communicated with SPP1 High macrophages via the C3–integrin pathway and with neutrophils via the CXCL12–CXCR4 pathway, whereas myCAF mainly communicated with monocytes and mast cells via ECM‐related pathways. Subsequently, we performed two panels of Opal multiplex immunohistochemistry and Elastic van Gieson staining to evaluate fibroblast and myeloid subpopulations and collagen, respectively, in all enrolled cases. Quantitative image analyses revealed that iCAF, neutrophils, and SPP1 + macrophages were associated with higher histological grade, whereas myCAF, collagen, monocytes, and mast cells were associated with lower histological grade. No decrease in myCAF or increase in neutrophils was observed in the invasive intestinal type. Finally, we classified the cases into three groups based on the density of fibroblast and myeloid subpopulations: iCAF/SPP1 + macrophage‐rich (I‐stroma), neutrophil‐rich (N‐stroma), and myCAF/mast cell‐rich (M‐stroma). These stromal groups were associated with distinct clinicopathological features. In conclusion, we revealed that the heterogeneous microenvironment of IPMN, associated with distinct clinicopathological features, may explain the clinical significance of histological subtypes. © 2026 The Pathological Society of Great Britain and Ireland.