Traditionally, it was suggested that genetic abnormalities in leukemia could be roughly grouped into two classes according to their roles in pathogenesis: Class I, mutations involving signal transduction pathways and giving rise to proliferative advantages to leukemia clones, exemplified as C-KIT, FLT3 and NRAS; and Class II, mutations affecting transcription factors (TF) or co-factors and causing impaired differentiation such as point mutation of CEBPA, AML1 and gene fusion of AML1-ETO [11]. Here, RUNX1 is linked to leukemia.