As a consequence, numerous HDAC inhibitors have undergone clinical trials and several have recently been approved by the FDA for use in various human cancers.15 It is hoped that these HDAC inhibitors can be used in tumours that have either developed resistance to conventional therapies or following relapse of the primary cancer.16 It has been clearly demonstrated that the patterns of global H3 and H4 acetylations correlate with the severity of prostate and other cancers,9 while global methylation patterns may have a diagnostic and prognostic potential for a range of different tumours.10 This evidence concerns the gene HDAC9 and cancer.