ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: BCR::ABL1 variants lacking ABL1 exon 2 occur in a minority of CML patients as a consequence of the chromosome 9 breakpoint occurring 3’ of this exon [6–9], and are referred to as BCR::ABL1/b2a3 or BCR::ABL1/b3a3 depending upon the presence or absence of BCR exon 14.