BCR and chronic myelogenous leukemia, BCR-ABL1 positive: According to previous reports, BCR is physiologically down-regulated upon myeloid maturation from hematopoietic stem cells (HSCs) to common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) and this mechanism is conserved in healthy donors and in CP-CML [39].