A California cancer consortium study revealed that SAHA alone failed to achieve success in the treatment of 14 patients with metastatic breast cancer.32 In our study, we observed that the pan-HDAC inhibitors SAHA and LBH589 promote breast cancer invasion and metastasis in vitro and in vivo, which in turn will impede the efficacy of HDAC inhibitors in breast cancer. The gene discussed is HDAC9; the disease is cancer.