HDAC9 and cancer: Growing evidence demonstrates that HDACs are overexpressed in a variety of primary human tumors [25], including breast cancer, and we also found that higher levels of specific HDACs are associated with a significantly poorer outcome in patients with either breast cancer (Supplementary Fig. 1a) or lung cancer (Supplementary Fig. 1b), justifying the potential use of HDAC inhibitors (HDACi) in cancer therapy.