Atypical chronic myeloid leukemia (aCML) is a heterogeneous disorder belonging to the group of myelodysplastic/myeloproliferative (MDS/MPN) syndromes. In aCML many clinical features (splenomegaly, myeloid predominance in the bone marrow but with dysplastic features without the pathognomonic Philadelphia chromosome . SETBP1 was identified as a novel oncogene in aCML.Activating mutations in the gene encoding the receptor for colony-stimulating factor 3 (CSF3R) have been found in patients with atypical CML.