The role of SOX9 in the chemoresistance has been reported in multiple tumours, for example, chondrosarcoma, breast cancer, glioblastoma, cervical cancer, gastric cancer and lung cancer.26–31 In cervical cancer cells, SOX9 was found to increase cancer cell chemoresistance through inhibiting miR-130a.27 However, the detailed mechanisms of how SOX9 contributes to chemoresistance have not been clarified to date. Here, SOX9 is linked to breast cancer.