Chronic myeloid leukemia (CML) is a distinct myeloproliferative neoplasm characterized by the BCR-ABL1 fusion gene, resulting from acquired balanced reciprocal genetic translocation, t(9;22) (q34;q11.2) happening in haemopoietic stem cells that result in the so-called Philadelphia (Ph) chromosome. The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.