PHGDH and neoplasm: Transcripts expressions of three key enzymes (phosphoglycerate dehydrogenase (PHGDH), phosphoserine phosphatase (PSPH), and phosphoserine aminotransferase (PSAT1)) involving in de novo serine synthesis, and two key enzymes that channel serine into folate-cycle as the cytosolic serine hydroxymethyltransferase 1 (SHMT1) and mitochondrial SHMT2, and the proton-coupled folate transporter (PCFT) are highly over expressed in T1 and T3 vs. T2 tumours (Figure 4C).