Presence of a BCR-ABL1 fusion gene is necessary for the pathogenesis of CML. In up to 95% of cases, a t(9;22) (q34;q11) translocation results in the BCR-ABL1 fusion gene (Faderl et al. 1999). This translocation results in the Philadephia chromosome. In rare CML cases lacking the traditional t(9;22) translocation, other translocations result in the creation of the BCR-ABL1 fusion gene, which sometimes involve multiple chromosomes.