RUNX1 is a recurrent target of somatic mutations in de novo AML, myelodysplastic syndrome (MDS), acute lymphocytic leukemia (ALL), atypical chronic myeloid leukemia (aCML), and secondary AML (Mangan and Speck, 2011). Here, RUNX1 is linked to atypical chronic myeloid leukemia, BCR-ABL1 negative.