HDAC9 and breast cancer: Interestingly, selumetinib (MEK inhibitor), vorinostat (HDAC inhibitor), crizotinib (ALK inhibitor), and palbociclib (CDK inhibitor) have already been successfully applied to treat patients with cancer, such as neurofibromatosis, lymphoma, multiple myeloma, and HER2-positive breast cancer (Fig. 2H).