Elevated expression of PHGDH is reported to be associated with tumor development in various tumors32 and poor prognosis in patients with cancers, including NSCLC.33 It was also reported to be involved in polarization and proliferation of M2 macrophage.34 Since deficiency of serine/glycine was reported to increase the enzmes for serine/glycine synthesis, including PHGDH,35 such negative feedback mechanisms might prevent direct correlation between the PHGDH expression and serine/glycine concentrations. This evidence concerns the gene PHGDH and cancer.