HDAC9 and hepatocellular carcinoma: Still, previous studies assessing single HDACs have shown an upregulation of the protein expression of different HDACs, such as HDAC1 [6], HDAC2 [7], HDAC3 [37], HDAC4 [10], HDAC5 [8], HDAC9 [38], HDAC6 [39] and HDAC11 [40] in human HCC tissues compared with non-tumorous liver tissues.