The breakpoints within BCR are mapped to a 5.8-kb area spanning exons 12 to 16, the major breakpoint cluster region (M-bcr), found in 90% of patients with CML and in 20 to 30% of patients with Ph-positive B-cell acute lymphoblastic leukemia (Ph+ B-ALL) [1-3]. This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.