RAD51 and breast cancer: In addition, miR-155 was reported to regulate DNA repair activity and sensitivity to IR by repressing RAD51 in breast cancer cells [18], and miR-34a/b/c-5p was shown to directly target the RAD51 mRNA 3′-UTR or indirectly inhibit RAD51 expression via the p53 signaling pathway, indicating that miR-34s overexpression reduces the efficiency of HR repair and induces DSBs by down-regulating RAD51 expression [19].