HDAC9 and cancer: Nevertheless, four pan-HDAC inhibitors, vorinostat, romidepsin, belinostat, and panobinostat, have been approved by the US FDA for treating cutaneous T cell lymphoma, peripheral T cell lymphoma, and multiple myeloma (Cappellacci et al., 2020); many clinical trials using other HDAC inhibitors are also underway to treat various diseases, especially cancers (Cappellacci et al., 2020).