DOT1L and leukemia: HOXA9 plays a key role in KMT2A-rearranged (KMT2A-r) leukemia (Faber et al., 2009; Orlovsky et al., 2011), mediated by binding of the KMT2A fusion protein to HOX gene promoters (Milne et al., 2002; Milne et al., 2005) and recruitment of DOT1L H3K79 methyltransferases (Bernt et al., 2011; Kerry et al., 2017).