HDACs, responsible for the removal of acetyl groups from histone lysine residues, have been reported to have abnormal expression in cancers, and HDAC inhibitors (HDACi) have been considered as potential drugs in cancer treatment (Audia and Campbell, 2016; Li and Seto, 2016; Peleg et al., 2016; San Jose-Eneriz et al., 2019; Mirzaei et al., 2020; Wang P. et al., 2020; Wang X. et al., 2020). The gene discussed is HDAC9; the disease is cancer.