Previous studies have shown evidence that HDAC inhibitors exert potent anti-metastatic activity.20,33–35 However, recently investigations demonstrated that HDAC inhibitors promote metastasis of hepatoma, melanoma, and colorectal cancer cells.36–38 Here, we determined that SAHA and LBH589 changed the shape of breast cancer cells to a fibroblast-like morphology, increased cells invasiveness, and promoted lung metastasis in vivo. The gene discussed is HDAC9; the disease is breast cancer.