HDAC9 and neoplasm: Chidamide, the first orally administered selective HDAC inhibitor targeting HDAC1, HDAC2, HDAC3, and HDAC10,160 is currently under investigation for a variety solid and hematological malignancies, autoimmune diseases, and neurodegenerative diseases.196–201 It offers advantages over pan-inhibitors in the treatment of tumor diseases and in minimizing severe adverse effects.160 Recent therapeutic strategies using chidamide in combination with a second antitumor intervention have shown promising prospects.