PHGDH and intrahepatic cholangiocarcinoma: Moreover, phosphoglycerate dehydrogenase (PHGDH), a rate-limiting enzyme in the Ser/Gly metabolic pathway, is upregulated in ICC in association with histone methyltransferase G9a, suggesting that activation of the Ser/Gly metabolic pathway is involved in the progression of ICC to malignancy102.