The Ph results in the formation of the BCR/ABL1 fusion gene, which is a constitutively activated tyrosine kinase.     ///    "BCR/ABL1 formation resulted from a direct insertion (one step mechanism) in 6 patients and CML-T1, while in 3 patients the fusion gene originated from a sequence of rearrangements (multiple steps). "    ///    Here we present FISH mapping data of BCR and ABL1 flanking regions and associated chromosomal rearrangements in 9 Ph negative BCR/ABL1 positive CML patients plus the cell line CML-T1.     ///    "Around 1% of CML patients appear to have a Ph negative karyotype but carry a cryptic BCR/ABL1 fusion that can be located by fluorescence in situ hybridisation (FISH) at chromosome 22q11, 9q34 or a third chromosome. "    ///    "BCR/ABL1 was located at 9q34 in 3 patients, 22q11 in 5 patients and CML-T1 and 22p11 in 1 patient. "    ///    FISH mapping of Philadelphia negative BCR/ABL1 positive CML..     ///    Future studies should be performed to confirm the presence of true breakpoint hot spots and assess their implications in Ph negative BCR/ABL1 positive CML.. 