HDAC9 and primary cutaneous T-cell non-Hodgkin lymphoma: HDAC inhibitors are already used in the clinic for treatment of CTCL (Mann et al., 2007; Jones et al., 2016; Wilcox, 2016; Lopez et al., 2018; Sermer et al., 2019; Chen et al., 2020; Lai and Wang, 2021b; Pavlidis et al., 2021).