PHGDH and cancer: For instance, Singh et al. showed that frequently overexpressed or amplified phosphoglycerate dehydrogenase (PHGDH) [56,57], an enzyme that catalyzes the rate-limiting step of glucose-derived serine synthesis, is heterogeneous across cancer cells of TNBC cell lines due to metabolic stresses from architecture [58] in addition to possible clonal heterogeneity.