HDAC inhibitors are known as effective therapeutic anticancer agents via multiple mechanisms, including the induction of cell-cycle arrest, differentiation, senescence, intrinsic and extrinsic apoptosis, mitotic cell death, autophagic cell death, generation of reactive oxygen species, inhibition of angiogenesis and metastasis, and improvement in tumor immunity [8, 51] (Table 1 and Figure 1). Here, HDAC9 is linked to neoplasm.