In addition, other studies showed that irradiation induced HER2 expression in HER2-negative breast cancer cells and that the HER2 induction was associated with HER2+/CD44+/CD24–/low BCSCs and radioresistance [10], which suggested that HER2 overexpression in HER2-negative breast cancer was associated with BCSCs and radioresistance. This evidence concerns the gene CD44 and breast cancer.