ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: The e13a2/e14a2 alternative transcripts (or b2a2/b3a2), which result from the juxtaposition of BCR exon 13 or 14 with ABL1 exon 2, produce a 210 kDa protein found in >90% of patients with CML (1).