Although increasing evidence has shown that pan‐HDAC inhibitors such as vorinostat and SB939 can reduce the occurrence of BCBM, it is still unclear which specific HDAC protein plays a key role in the process of breast cancer cell metastasis to the brain and whether such effect is directly caused by a particular HDAC protein or derived from HDAC downstream gene targets. The gene discussed is HDAC9; the disease is breast carcinoma.