Histone deacetylases (HDACs), the cellular enzymes whose functions include turning gene expression off and on, are promising targets in current drug development for cancer therapy. While treatment with HDAC inhibitors as monotherapies has demonstrated clinical benefit for patients with various hematological and solid tumor malignancies, there is excitement surrounding early results of their use together with other cancer therapeutics. That has spurred an increase in the research and development of treatment combinations with therapeutics such as checkpoint inhibitors.