First, we analyzed the mRNA expression of all HDAC class I (HDAC 1, 2, 3 and 8), class IIa (HDAC 4, 5, 7 and 9), class IIb (HDAC 6 and 10) and class IV (HDAC 11) in four different human HCC cell lines (Hep3B, HepG2, Huh7 and PLC) and primary human hepatocytes (PHH) with quantitative PCR. The gene discussed is HDAC9; the disease is hepatocellular carcinoma.