**3.3 Cytogenetics**

The cytogenetic picture of CML provides unique and crucial information for diagnosis. Cytogenetic analysis of bone marrow or peripheral blood cells allows the identification of the Ph translocation and other chromosome changes that are associated with the leukemic process. Diagnostic assays at baseline for CML patients are based on the standard banding cytogenetics (chromosome banding analysis or CBA) and fluorescence in situ hybridization (FISH) [39].

Cytogenetic examination is preferably performed on bone marrow cells. The t (9; 22) (q34; q11) is easily recognized when the cell cycle of leukemic cells is disrupted in the metaphase. Identification of translocation 9; 22 requires analysis of at least 20 metaphases [40].

The FISH technique is used when the result is urgent. Fast and specific, this technique allows detection of *BCR-ABL* rearrangement through the use of molecular probes [37].
