PDE4D and cholangiocarcinoma: A prognostic model (including ALDH3B2, RACGAP1, SH3PXD2A, PDE4D, SCAPER and STX18) was constructed for cholangiocarcinoma patients according to the differentially expressed eccDNA-related genes in the bile to further analyze the function of eccDNA annotated genes and the regulation of cholangiocarcinoma.