HDAC9 and cancer: In line with this notion, epigenetic drugs, including azacitidine, decitabine, EZH2 blockers and multiple HDAC inhibitors, are currently approved for use in cancer patients, often in malignancies with abundant stem cell compartments, such as hematological tumors.13,14 However, a number of questions remain to be answered to unlock the full therapeutic potential of CSC-targeted epigenetic drugs.