In such ‘MRD discordant’ cases, BCR-ABL1 positivity was found to reside in non-ALL B-lymphocytes, T-cells, and/or myeloid cells, suggesting that a multipotent hematopoietic progenitor cell was the source of the translocation [55,56], resulting in a more CML-like clinical picture. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.