While BCR-ABL-based subclassification and associated target therapy remain the standard care for CML patients, there is growing evidence showing that a minority of mutational subclones within CML are highly resistant to tyrosine kinase inhibitors,22, 23, 24 suggesting that subclassification based on intertumor heterogeneity may not capture the full tumor spectrum. Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.