In 95% of CML cases, the product of a reciprocal translocation between chromosomes 9 and 22, the Philadelphia chromosome, is detected, which is characterized by the presence of Bcr–Abl fusion gene, representing a subtype of leukemia with poor prognosis, rapidly acquiring resistance to the Imatinib treatment during therapy [12, 13]. The gene discussed is ABL1; the disease is leukemia.