Although HDAC inhibitors such as panobinostat are broadly active in many haematopoietic tumours, including ALL11 (data for non-MEF2D ALL subtypes are shown in Supplementary Fig. 17) and are being explored as a therapeutic option for a range of relapsed and refractory tumours, we observed exquisite sensitivity in MEF2D-rearranged ALL (Fig. 4c). Here, HDAC9 is linked to acute lymphoblastic leukemia.