From the perspective of cancer research, DOT1L has been perceived as a promising therapeutic target for mixed lineage leukemia (MLL)-rearranged leukemia since DOT1L was found to be recruited by various MLL-fusion proteins to MLL target genes such as HOXA9 and MEIS1, resulting in aberrant H3K79 methylation and consequential expression of these leukemogenic genes [13–15]. The gene discussed is DOT1L; the disease is leukemia.