Up-regulation of histone deacetylase 3 (HDAC3) promoted GEM resistance in pancreatic cancer cells via modulation of cell cycle- and apoptosis-related genes and two HDAC inhibitors trichostatin A and 4-phenylbutyrate inhibited the proliferation of pancreatic cancer cells and enhanced the sensitivity to GEM [18–20]. The gene discussed is HDAC9; the disease is pancreatic neoplasm.