CML in blast crisis: more common than we think?

In this issue of Blood, Hovorkova and colleagues assessed minimal residual disease (MRD) sequentially in children with Philadelphia chromosome positive acute lymphoblastic leukemia (Ph ALL) via BCR-ABL1 genomic polymerase chain reaction (PCR) and immunoglobulin gene (IG)/T-cell receptor gene (TCR) PCR in parallel. Results were concordant in most patients, but .20% of children with Ph ALL had MRD levels that were .1 log higher with BCR-ABL1 genomic PCR than with IG/TCR PCR. Using cell sorting and fluorescence in situ hybridization (FISH) to study patients with discordant MRD results, the authors demonstrated conclusively that BCR-ABL1–positive cells were present in nonmalignant B cells, T cells, and myeloid cells, establishing that the translocation occurred in a multipotent hematopoietic progenitor cell and suggesting that these patients have a disease more akin to chronic myeloid leukemia (CML) in lymphoid blast crisis than Ph ALL.