HDAC6 and hematopoietic and lymphoid system neoplasm: Citarinostat (ACY-241) is a second-generation, bioavailable, and selective inhibitor of class IIb histone deacetylase 6 (HDAC6) [20] that is active against MM [10,21] and acts synergistically in combination with other therapeutic agents against solid tumors and blood cancers [25,26,27,28,29].