Indeed, the active P-TEFb-Brd4 complex has been linked to AML and CML (Dawson et al., 2011; Mertz et al., 2011; Zuber et al., 2011; Herrmann et al., 2012; Winter et al., 2012), while multiple SEC components are direct targets of MLL-fusion proteins that are linked to various forms of leukemia (Lin et al., 2010; Yokoyama et al., 2010). Here, KMT2A is linked to chronic myelogenous leukemia, BCR-ABL1 positive.