Unique stroma of higher-grade pancreatic intraepithelial neoplasia: Fibroblastic cluster formation and CD36-downregulation

Introduction: Identifying pathological markers to differentiate between high- and low-grade pancreatic intraepithelial neoplasia (PanIN) remains an unmet clinical need. Recent studies suggest that the tumor microenvironment undergoes dynamic changes during PanIN progression. To establish objective pathological markers, this study investigated histological, immunohistochemical, and molecular alterations in PanIN-associated stroma across different grades. Methods: Fibroblastic cluster (FC) was defined and characterized using immunohistochemistry (IHC) for SMA, CD31, and CD34, and their frequency was assessed according to PanIN grade in 202 PanIN lesions and 58 normal ducts. To identify molecular differences among PanIN types, multiple gene expression analysis (MGEA) was performed for six normal ducts, and for three PanIN1, three PanIN2, and six PanIN3 lesions. IHC and fluorescent dual IHC for CD31 and CD36 were performed to quantify CD36-positive stromal vessels. RNA scope for PPAR and IHC for thrombospondin-1 (TSP-1) and forkhead box O1 (FOXO-1) were performed to explore the molecular basis of CD36 downregulation. Results: FCs were identified in 86.6% of PanIN3 stroma and were significantly more frequent than in lower-grade PanINs. MGEA revealed downregulation of CD36 in PanIN2-3 compared with PanIN1, and CD36-positive vessels were significantly fewer in higher-grade PanIN stroma. PPAR signals were present in low-grade but absent in high-grade PanIN stroma. TSP-1 expression paralleled CD36 expression. These findings suggest that the possible relationship between the repression of CD36 in the stromal vasculature of high-grade PanIN and reduced PPAR and TSP-1 signaling. Conclusions: Higher-grade PanINs harbor a unique stroma characterized by FC formation and an increased proportion of CD36-negative vessels.