M-bcr breakpoints occur downstream of exon 13 (e13) or exon 14 (e14) of the BCR gene, producing the p210 fusion protein, which is found in 97–99% of CML cases and in 40% of adult and 10% of pediatric B-lymphoblastic leukemia/lymphoma (B-ALL) patients. This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.