Chronic myeloid leukaemia is a haematologic malignancy associated with a balanced reciprocal translocation between the Abelson leukaemia virus gene (ABL) on chromosome 9 and the break-point cluster region gene (BCR) on chromosome 22 forming the BCR-ABL fusion gene. The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.