To evaluate whether radiosensitization with combined HDAC inhibition and RT can increase the vulnerability of HCC cells and consequently enhance their susceptibility to NK cell-mediated cytotoxicity, the pan-HDAC inhibitor, panobinostat (LBH589) or HDAC4 knockdown combined with various doses of RT were used for the clonogenic survival by co-culture system. The gene discussed is HDAC9; the disease is hepatocellular carcinoma.