HDAC9 and plasma cell myeloma: Modern treatment of multiple myeloma is based on five pillars: a) immunomodulatory drugs (IMiDs) (i.e. lenalidomide, pomalidomide and thalidomide); b) proteasome inhibitors (i.e. bortezomib, MG-132 and carfilzomib); c) traditional cytotoxic drugs (i.e. doxorubicine); d) HDAC inhibitors (i.e., vorinostat or panobiostat) and e) corticosteroids (e.g., dexamethasone and prednisone).