Based on the unique features of HDAC inhibitors and gold nanoparticles, we hypothesized that the HDAC inhibitor SAHA could further potentiate the radiosensitizing action of AuNPs and vice versa, AuNPs can increase the radio-enhancing features of SAHA, resulting in a synergistically augmented tumor eradication potency of combinational cancer therapy. This evidence concerns the gene HDAC9 and cancer.