ATF4 and cholangiocarcinoma: Last but not least, the transcriptomic analysis of serum EVs from CCA versus PSC patients demonstrated several mRNA transcripts as potential biomarkers for CCA differentiation from PSC, including phosphoglycerate dehydrogenase (PHGDH), activating transcription factor 4 (ATF4), and paraoxonase 1 (PON1), presenting an optimal AUC value of 1.00 as the differentiation method for CCA versus PSC patients [106].