For example, combinations of HDAC-HSP90 inhibitors (104), HDAC-DNMT inhibitors (105), HDAC-KDM1 inhibitors (106), HDAC-BET protein inhibitors (107, 108), HDAC-EZH2 inhibitors (109), and HDAC-PI3K inhibitors (110) showed good efficacy in different cancer cells. This evidence concerns the gene HDAC9 and cancer.