HDAC9 and bone neoplasm: It was reported that the HDAC inhibitor trichostatin A evinced antinociceptive activity on bone cancer pain by restoring μ-opioid receptor expression [36]; expressions of certain HDACs were ascertained, revealing that the HDAC2 expression was enhanced in the spinal cord tissues in a time-dependent manner and that trichostatin inhibited HDAC2 expression in PC12 cells.