The majority of breakpoints on the BCR side occur in two “breakpoint cluster regions” – “minor” (between exons 1 and 2; ~ 71.5 kilobase pairs [kbp], resulting in the p190 fusion protein, prevalent in ALL and scarce in CML) and “Major” (between exons 13 and 15; ~ 2.9 kbp, resulting in the p210 fusion protein, less frequent in ALL and almost exclusive in CML). This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.