###Human: Why would I be BCR-ABL positive and Philadelphia chromosome negative? ###Assistant: Hello. Chronic myeloid leukemia (CML) is a hematopoietic disorder, almost always characterized by the presence of the Philadelphia chromosome (Ph), usually due to t(9;22)(q34;q11) or its variants. The Ph results in the formation of the BCR/ABL1 fusion gene, which is a constitutively activated tyrosine kinase. 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 hybridization (FISH) at chromosome 22q11, 9q34 or a third chromosome. Hence, the cytogenetic profile is normal by karyotyping in Ph-negative patients but they have the BCR/ABL fusion gene which is detected by molecular methods like FISH and PCR. For further queries consult a hematologist online -->