There are already ongoing clinical trials with HDAC inhibitors in cancer, the miR-122 inhibitor miravirsen in chronic HCV, and first-into-man trials with a mimetic of miR-34, a powerful tumor suppressor.57,58 But again, enthusiasm must be tempered with what are significant hurdles to be overcome, not the least in finding drugs with sufficient specificity for a given epigenetic modifier to ensure efficacy and prevent clinical toxicities. Here, HDAC9 is linked to cancer.