In leukaemia research, cell lines, such as the BCR/ABL-positive K562 myeloid cell line, derived from a chronic myeloid leukaemia (CML) patient in blast crisis, or the leukaemic t(15;17)-positive NB4 cell line, derived from a patient with acute promyelocytic leukaemia (APL), are often used to study the molecular pathology of CML and APL respectively. The gene discussed is BCR; the disease is acute promyelocytic leukemia.