ERBB2 and breast cancer: The biological role of miR‐200c in tumour cells and stem cells has been demonstrated in many cancers.27 To further explore the role of miR‐200c in HER2‐overexpressing breast cancer, we first compared the expression of miR‐200c in 9 breast cancer cells and 1 mammary epithelial cell line and in CD44+CD24− phenotype stem cells of the above 10 cell lines.