In conclusion, these results are consistent with our hypothesis that miR‐200c reduces stemness and increases sensitivity to trastuzumab in HER2+ breast cancer cells and stem cells via inhibition of Jagged1, ZEB1 and Bmi1, which are three important genes in the stemness‐related Notch, Wnt and Hedgehog pathways. This evidence concerns the gene JAG1 and breast cancer.