A practical distribution pattern of α-SMA-positive carcinoma associated fibroblasts indicates poor prognosis of patients with pancreatic ductal adenocarcinoma

Purpose The present study aimed to clarify the distribution pattern of carcinoma associated fibroblasts (CAFs) across pancreatic ductal adenocarcinoma (PDAC) and its prognostic prediction value. Methods Data of two cohorts were retrospectively collected from consecutive patients who underwent primary pancreatic resection from January 2015 to December 2017. We used tumor specimens to screen out the most suitable markers for the spatial distribution analysis for CAFs subpopulations. We utilized a tissue microarray to assess the spatial intensity of α-SMA expression within the tumor microenvironment. Specifically, we classified CAFs into two types based on their α-SMA spatial expression. Type II CAFs were designated as those located in the juxtatumoural stroma with α-SMA expression that was moderate or higher, and those in the peripheral stroma with α-SMA expression that was less than moderate. All other cases, where the α-SMA expression did not meet these criteria, were categorized as Type I CAFs. Multivariable Cox proportional hazards regression was used to assess risk factors associated with patient outcomes. RNA sequencing data were obtained from bulk tumor samples and isolated CAFs from patients to reveal the distinct pattern and elucidated their fundamental characteristics. Results The α-SMA spatial intensity was the most suitable variable for representative of CAFs spatial characteristics. Patients with Type Ⅰ CAFs were more likely to be allocated into N1 or N2 of the N stage and Ⅱ and Ⅲ of the TNM stage. The spatial distribution pattern of CAFs (Type Ⅰ v.s. Type Ⅱ: HR, 1.568; 95 % CI, 1.053-2.334; P = 0.027) was an independent prognostic factor in the discovery cohort, so as in the validation (Type Ⅰ vs. Type Ⅱ: HR, 2.197; 95 % CI, 1.410-3.422; P = 0.001). RNA sequencing analysis revealed that the differentially expressed genes (DEGs) in Type I CAFs are closely associated with those in corresponding tumor tissues, highlighting the enhanced biological significance of immune-related and oncogenic invasive pathways. Conclusions Our findings that two types of α-SMA-positive CAFs with different spatial patterns present heterogeneously across tissues of PDACs and correlated with patients' outcomes. The spatial location of CAFs may facilitate patients' selection in precision medicine of PDACs.