HDAC9 and hematologic disorder: Up to date, there are six HDAC inhibitors (Figure 1) have been FDA-approveed; Vorinostat (SAHA) 1 [12], Romidepsin (FK228) 2a and its active metabolite RedFK 2b [13], Belinostat (PXD101) 3 [14], Pracinostat 4 [15], Panobinostat (LBH-589) 5 [16] are approved by the FDA while (Chidamide) 6 is approved by the Chinese FDA for the therapy of hematological malignancies (CS055) [17,18].