BCR and chronic myelogenous leukemia, BCR-ABL1 positive: For example, in a patient with a BCR::ABL1pos CML emerging in a pre-existing JAK2 V617F MPN, analyses of pooled CFU-GM and BFU-E identified BCR::ABL1 only in CFU-GM but not in BFU-E while JAK2 V617F was identified in both compartments suggesting earlier acquisition of JAK2 V617F at the stem cell level20.