PIK3CA and breast cancer: The MDA‐MB‐231 is a PIK3CA‐mutant human breast cancer cell line that was reported to be sensitive to glutamine restriction.[21] Consistent with the result of GLS knockdown study, the PIK3CA‐mutant cell lines were not remarkably more sensitive to CB‐839 treatment than the wildtype cell lines, with growth inhibitory 50% (GI50) of 8.03 μM (HCT116), 7.93 μM (MDA‐MB‐231), 15.78 μM (MC38), 16.25 μM (CT26), and 15.76 μM (SW480), respectively (Figure 1D).