PHGDH and cancer: Decreased activity of key TCA cycle enzymes like isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and α-ketoglutarate dehydrogenase (α-KGDH) have been described in various cancers including gastric cancer [22,23], which is consistent with our findings.