circRNA expression profile in PDAC. (a) The volcano plot was constructed according to the fold change and p value. The x-axis presents the log2(fold change) value of differential expression, and the y-axis presents the -log10(padj) value of differential expression. The vertical lines correspond to 2.0-fold up- and downregulation between PDAC and adjacent nontumor tissues, and the horizontal line represents a p value of 0.05. The red circles in the plot represent the upregulated circRNAs, and the green circles in the plot represent the downregulated differentially expressed circRNAs with statistical significance. (b) Hierarchical clustering analysis of circRNAs that were differentially expressed (over a 2.5-fold change) between PDAC and adjacent nontumor tissues. The x-axis presents samples (N1-N5: adjacent nontumor tissues; T1-T5: PDAC tissues), and the y-axis presents the differentially expressed circRNAs. Expression values are represented in different colors; red indicates a high expression level, and blue indicates a low expression level.