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). Here, PHGDH is linked to cholangiocarcinoma.