ABL1 and acute myeloid leukemia: The most important change is that the 20% blast cutoff is not required in both classifications to define AML, except for AML with the Breakpoint Cluster Region (BCR): ABL Proto-Oncogene 1, Non-Receptor Tyrosine Kinase (ABL1) in both classifications, for CEBPA mutations in the WHO classification, AML-Myelodysplasia-related (MR) and AML-NOS defined by differentiation.