ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Most CML cases harbor a BCR::ABL1 fusion gene encoding the 210-kDa BCR::ABL1 protein, which arises from e13a2 (b2a2) and/or e14a2 (b3a2) junctions depending on the breakpoint location within the BCR gene (3).