Chronic myeloid (myelogenous) leukemia (CML) is a myeloproliferative disorder characterized by increased proliferation of the granulocytic cell line without the loss of their capacity to differentiate. Consequently, the peripheral blood cell profile shows an increased number of granulocytes and their immature precursors, including occasional blast cells.

It is the result of a reciprocal translocation between chromosome 9 and 22, and is specifically CML is one of the few cancers known to be caused by a single, specific genetic mutation. More than 95% of cases result from a cytogenetic aberration known as the Philadelphia chromosome. Philadelphia chromosome is a specific chromosomal abnormality that is associated with chronic myelogenous leukemia (CML). It is the result of a reciprocal translocation between chromosome 9 and 22, and is specifically designated t (9:22) (q34:q11). The detection of this translocation revealed by Reverse Transcription Polymerase Chain Reaction (RT-PCR). This assay is perform to diagnose the BCRABL/9:22 translocation in suspected patients of Chronic Myeloid Leukemia (CML).