ATF4 and cholangiocarcinoma: In particular, the mRNA transcripts paraoxonase 1 (PON1), activating transcription factor 4 (ATF4), and phosphoglycerate dehydrogenase (PHGDH) stood out as the best candidate biomarkers for the differential diagnosis of CCA and PSC, all with AUC values of 1.00 (Figure 3B).