HDAC9 and cancer: Previous studies have elucidated pathways regulated by HDACs and counteracted by HDAC inhibitors in cancer, including PTEN/Akt/mTor, p53, p21, p27 as well as cyclin/Cdk complexes, which when inhibited lead to the enhancement of cell cycle arrest and apoptosis that is observed with HDAC inhibitors [15, 18, 19].