Chronic myeloid leukemia (CML) is a slow-growing myeloproliferative neoplasm characterized in more than 95% of cases by the t(9;22) (q34.1;q11.2) chromosomal translocation leading to the formation of the Philadelphia chromosome (Ph*), resulting in the BCR-ABL1 gene fusion. The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.