HDAC9 and glioblastoma: Various HDAC inhibitors, such as panobinostat, vorinostat and valproate, have shown potent efficacy against GBM in preclinical studies, and multiple anti-GBM mechanisms, including the induction of cell cycle arrest, differentiation, apoptosis, autophagic cell death, generation of reactive oxygen species, inhibition of angiogenesis and DNA damage repair (DDR), have been suggested [6–8].