HDAC9 and acute myeloid leukemia: On the other hand, in multiple myeloma, acute myeloid leukemia/myelodysplastic syndromes (AML/MDS) and other high-risk hematological malignancies, the HDAC inhibitor has been used in combination with proteasome inhibitor bortezomib, anti-CD20 antibody rituximab and anti-CD22 antibody epratuzumab with promising synergistic activities and good tolerance [26,27,28].