CSF3R and atypical chronic myeloid leukemia, BCR-ABL1 negative: CSF3R mutations, which were discovered in 2013, are shared by aCML and chronic neutrophilic leukemia, a rare subtype of myeloproliferative neoplasms (MPN) characterized by neutrophilia with less than 10% immature precursors in the peripheral blood.1, 4, 5SETBP1 mutations are also found to be closely related to the aCML phenotype.