ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: According to the European Leukemia Network (ELN) guidelines for chronic myeloid leukemia (CML), BCR-ABL1 transcript levels (addressed as BCR-ABL1 throughout) of ≤10% according to the international scale (IS, BCR-ABL1IS) in the peripheral blood or a partial cytogenetic response (pCyR), <35% Philadelphia (Ph)+ metaphases, are defined as optimal treatment response at 3 months [1].