As noted previously14,27, the response to serine and glycine starvation varied between cell lines ranging from RKO, HT-29 and SW48 cells that showed a significant dependence on exogenous serine and glycine for proliferation, to DLD-1, LoVo, CACO-2 and MDA-MB-468 cells (a breast cancer line previously shown to carry PHGDH amplification) that were not affected by lack of serine and glycine in the medium (Fig. 1b and Supplementary Figure 1a). This evidence concerns the gene PHGDH and breast cancer.