Traditionally, the HDAC protein family plays a key role in the regulation of the cell cycle, cell differentiation, apoptosis, migration and invasion, and angiogenesis by increasing histone acetylation; while HDAC inhibitors can nonselectively inhibit all or multiple members in the family to produce an anti-cancer effect in various cancers including NETs [18,19,20,21,22]. The gene discussed is HDAC9; the disease is cancer.