To validate the role of NOTCH1/HEY1 pathway on mediating CXCL2-induced breast cancer cell stemness, 4T1 cells were treated with rmCXCL2 and NOTCH inhibitor RO4929097, a γ-secretase inhibitor to reduce NICD1 by blocking transmembrane proteolytic cleavage.43 The increase of ALDH+ BCSCs induced by rmCXCL2 was inhibited in 4T1 cells under RO4929097 treatment (Fig. 5g). This evidence concerns the gene NOTCH1 and breast cancer.