Chronic myeloid leukemia (CML) is a disease that arises in hematopoietic stem cells and is caused by a reciprocal translocation between chromosomes 9 and 22 (t(9;22)(q34;q11.2)), referred to as the Philadelphia chromosome, which generates BCR-ABL1 fusion transcripts. The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.