Pan-HDAC inhibitors have pleiotropic effects in CTCL and exact mechanism(s) by which they affect cell viability of CTCL cells is not completely known, although it has been shown that combined treatment of an HDAC inhibitor with a demethylating agent led to re-expression of a tumor suppressor gene and induction of apoptosis in CTCL cell lines (Duvic, 2015; Rozati et al., 2016; Moskowitz and Horwitz, 2017; Lopez et al., 2018; Chen et al., 2020). This evidence concerns the gene HDAC9 and primary cutaneous T-cell non-Hodgkin lymphoma.