Although the exact mechanism of HDAC inhibitor treatment in CTCL is not known, several HDAC inhibitors, including Vorinostat, Panobinostat and Romidepsin, have been approved or are currently in clinical trials for CTCL treatment (Mann et al., 2007; Ellis et al., 2008; Duvic et al., 2013, 2018; Barbarotta and Hurley, 2015; Jones et al., 2016; Lopez et al., 2018; Sermer et al., 2019; Chen et al., 2020; Lai and Wang, 2021b; Pavlidis et al., 2021). The gene discussed is HDAC9; the disease is primary cutaneous T-cell non-Hodgkin lymphoma.