BDNF and pancreatic adenocarcinoma: To further verify the significant differential infiltration levels of Th2 cells in PAAD patients stratified by BDNF expression levels, the TCGA-PAAD cohort and GSE85916 and ICGC PAAD-AU cohort were used to evaluate the levels of Th2 cells in the high BDNF expression and low expression subgroups as internal validation and external validation, respectively.