NAT8B and chronic myelogenous leukemia, BCR-ABL1 positive: On the other hand, the breakpoints in the CML cases were located as expected in the major breakpoint cluster region from BCR (intron 14 in CML1 and intron 13 in CML2) and in the first intron of ABL1 (Table 1) and result in the p210 BCR-ABL1 fusion characteristic of CML.