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. The gene discussed is ABL1; the disease is acute lymphoblastic leukemia.