BCR and chronic myelogenous leukemia, BCR-ABL1 positive: In the majority of CML cases, the BCR-ABL fusion junction contains a breakpoint in the M-bcr region at exon e13 (b2) or exon e14 (b3) and the oncogene is translated into one of two 210-kDa proteins (p210BCR-ABL) differing by 25 amino acids depending on the exons included.